- Use madvise when setting no permissions on memory.
- Move platform specific mmap flag calculations to a helper fn.

Bug: chromium:756050,chromium:788341
Change-Id: I7d420a0abee9656a57fb0317301322da2fd7d7b5
Reviewed-on: https://chromium-review.googlesource.com/790932
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49681}

This reverts commit 90405027.

Reason for revert: Flaky msan:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/18432

Original change's description:
> [heap] Tune incremental marking step size.
> 
> The main thread now can reduce marking step size if concurrent marking
> tasks are making progress and the bailout worklist is empty.
> 
> Bug: chromium:694255
> Change-Id: I2f58530f184c03667ab3a170a1f6309929645c7c
> Reviewed-on: https://chromium-review.googlesource.com/735859
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49671}

TBR=ulan@chromium.org,mlippautz@chromium.org

Change-Id: Ic10ee9bae51b2b4b78d87c83c67b1307d0c36012
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:694255
Reviewed-on: https://chromium-review.googlesource.com/794190Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49680}

This way it can already be used during deserialization.

Bug: v8:7133
Change-Id: I6d6ddb6c6e5326384d014d653b163f3d917089e9
Reviewed-on: https://chromium-review.googlesource.com/793393Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49679}

Use memmove if source and target are either Uint8Array or Uint8ClampedArray.

Bug: v8:7123,chromium:759236
Change-Id: If82bf10165cfc67274f36bb772ce9676a768dcc8
Reviewed-on: https://chromium-review.googlesource.com/790756
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49678}

- Use integer log2
- Fix lower bucket index
- Introduce upper bucket index

Bug: v8:7133
Change-Id: I1f1209a13d69ed6e27eeb18254fccb8263f62954
Reviewed-on: https://chromium-review.googlesource.com/793450Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49677}

Bug: 
Change-Id: Idca921bde6f10d8e9809c0b3a83cc3a8d3f135af
Reviewed-on: https://chromium-review.googlesource.com/779424
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49676}

R=hpayer@chromium.org
BUG=v8:6792,chromium:774108

Change-Id: I202993ddf5bb11d238ed173197657c6546dd4a37
Reviewed-on: https://chromium-review.googlesource.com/789865Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49675}

AggregatableHistogramTimer will always add a sample when it is destroyed,
even if there were no AggregatedHistogramTimerScope called within it. This
makes the V8.CompileLazyMicroSeconds histogram not particularly useful since
it is 90% filled with zero entries where v8 execute didn't require any
lazy function compilation

Change-Id: Ia75c8596237b22528cbba3e8ae2b67e28ea54097
Reviewed-on: https://chromium-review.googlesource.com/793452Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49674}

These fields relied on the assumption that 64-bit big-endian
architectures had sizeof(int) == 4. Any architecture violating this
assumption would result in an OOB access.

Bug: 
Change-Id: I682ecb6a2da2cf84e8b24f1c1e608d7fc23f5bdc
Reviewed-on: https://chromium-review.googlesource.com/793431Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49673}

See https://tc39.github.io/proposal-class-fields/#sec-static-semantics-early-errors

Bug: v8:5367
Change-Id: I0329d1b41c4658b733df47397fbcc2c16bad117e
Reviewed-on: https://chromium-review.googlesource.com/792946
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49672}

The main thread now can reduce marking step size if concurrent marking
tasks are making progress and the bailout worklist is empty.

Bug: chromium:694255
Change-Id: I2f58530f184c03667ab3a170a1f6309929645c7c
Reviewed-on: https://chromium-review.googlesource.com/735859
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49671}

Many methods which currently receive a {ValueType} really just need to
know the register class. Thus introduce a {RegClass} enum with values
{kGpReg} and {kFpReg}, and change some methods to use it. For most
methods, only the {kGpReg} case is implemented for now. Support for
{kFpReg} will be added later.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: I1db793c59270862c4e1b877e6e4bd81020a650f8
Reviewed-on: https://chromium-review.googlesource.com/793159Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49670}

This CL adds the --trace-wasm-lazy-compilation flag, to track which
function is being compiled, and how many locations in the caller and in
function tables are actually being patched.
It seems that we currently don't patch the caller correctly when
calling through wasm-to-wasm stubs, and this tracing helps to find the
issue.

Drive-by: Fix order and location of macro undefs.

R=titzer@chromium.org

Bug: chromium:788441
Change-Id: I6091c0d490a729f8e3cb759cd661cf52129d2211
Reviewed-on: https://chromium-review.googlesource.com/793157Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49669}

On 64-bit architectures, an IntPtr-sized write of Name::kEmptyHashField
will properly initialize the relevant Int32-sized payload of
Name::kHashFieldOffset, as well as zero out the unused portion of the
slot.

Bug: v8:7065
Change-Id: I93113c9744377e76cd0d264568c49b31a1e822a1
Reviewed-on: https://chromium-review.googlesource.com/788530Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49668}

We'd sometimes forget that the input was not originally a numeric.

Bug: v8:7135
Change-Id: I8bc690cc0c2dfac8a2a218ca56352b6a569825dc
Reviewed-on: https://chromium-review.googlesource.com/793039Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49667}

This is reland of 3e0bf580
Original change's description:
> This commit is a step toward enabling test-run-wasm-simd tests for MIPS.
> 36 of those were failing in V8 builtin simulator because some instructions
> were not implemented.  Also there are minor fixes to some of the already
> implemented instructions.
>
> This commit has only 32-bit implementation. After review I will add
> 64-bit version.
>
> Bug:
> Change-Id: I25b0cac352db3efb56b922ace64ab2aaef82472d
> Reviewed-on: https://chromium-review.googlesource.com/744008
> Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
> Cr-Commit-Position: refs/heads/master@{#49439}

Bug: 
Change-Id: I3a904caf675d314186c02c1c843d1e6a91a21a14
Reviewed-on: https://chromium-review.googlesource.com/776813Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#49666}

Bug: v8:5367
Change-Id: Ib24190f6cfc0765794a1a5d9ac33cf1c1e2b6fba
Reviewed-on: https://chromium-review.googlesource.com/793150Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49665}

Properly handle known JSBoundFunction instances as targets to
JSConstruct by inlining the construction of the eventual target.
Also if the target is the result of a JSCreateBoundFunction call,
where we can also fold the construction and construct the bound
target function directly instead.

This addresses half of the TODO in the JSConstruct lowering in the
JSCallReducer where so far we didn't handle bound functions.

Bug: v8:5267, v8:7109
Change-Id: I022dc7d4fbbe2c9972472e78a6d64f51e3134c94
Reviewed-on: https://chromium-review.googlesource.com/792947Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49664}

This reverts commit 61367a25.

Reason for revert: http://shortn/_amqTfxgjk0

Original change's description:
> [platform][cleanup] Fix --enable-tracing
> 
> The flag --enable-tracing can be used to measure how much time is spent
> in a scope. In d8 this flag did not work properly for the following
> reasons:
> 
> * The tracing file is not written when the JavaScript code calls quit().
> 
> * The tracing file is not written when the JavaScript code throws an
> uncaught exception, except if the --throws flag is passed to d8.
> 
> The reason for these two issues is that both call Shell::Exit(), which
> end d8 immediately without calling any destructors. In addition I moved
> in a recent CL the destruction of the platform after the destruction of
> the file handle for the tracing file. Thereby the tracing file did not
> get filled with content even destructors were executed.
> 
> With this CL I also call the destructors of the platform and of the file
> handle in the Shell::Exit() function. For this I make Shell::Exit()
> platform independent and let it call the platform dependent
> Shell::OSExit() at the end.
> 
> R=​rmcilroy@chromium.org
> 
> Change-Id: I14425b6a5c25b757211bc8b9959a9cc8bfa0602c
> Reviewed-on: https://chromium-review.googlesource.com/789038
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Commit-Queue: Andreas Haas <ahaas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49659}

TBR=rmcilroy@chromium.org,ahaas@chromium.org

Change-Id: I17c6f19c38cb337b00707f606f267b52b7f2c1e6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/792991Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49663}

In a recent CL I introduced module-level CodeSpaceMemoryModificationScopes,
which means that the number of CodeSpaceMemoryModificationScopes which
are opened aside from TurboFan compilation is not linear in the number
of functions anymore. In that CL, however, I did not remove scopes which
became obsolete. This CL removes now these obsolete scopes, and
introduces some scopes where shared code was used from outside the
compilation logic.

R=mstarzinger@chromium.org, clemensh@chromium.org

Bug: chromium:787731
Change-Id: I37d514efa3a4b10adb7008986a9c91e4557ce618
Reviewed-on: https://chromium-review.googlesource.com/790490
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49662}

Change the existing uses of the harmony-class-fields flag to
harmony-public-fields so that we can stage this separately
from the upcoming harmony-private-fields to get some
clusterfuzz coverage.

Bug: v8:5367
Change-Id: I76cdefa4faf34eae73d3a5f6d6089cf75677732a
Reviewed-on: https://chromium-review.googlesource.com/792940
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49661}

Bug: v8:5367
Change-Id: Ic725c5ef22ab05891764d3ebf9a99c0d383e6d90
Reviewed-on: https://chromium-review.googlesource.com/789939Reviewed-by: Mythri Alle <mythria@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49660}

The flag --enable-tracing can be used to measure how much time is spent
in a scope. In d8 this flag did not work properly for the following
reasons:

* The tracing file is not written when the JavaScript code calls quit().

* The tracing file is not written when the JavaScript code throws an
uncaught exception, except if the --throws flag is passed to d8.

The reason for these two issues is that both call Shell::Exit(), which
end d8 immediately without calling any destructors. In addition I moved
in a recent CL the destruction of the platform after the destruction of
the file handle for the tracing file. Thereby the tracing file did not
get filled with content even destructors were executed.

With this CL I also call the destructors of the platform and of the file
handle in the Shell::Exit() function. For this I make Shell::Exit()
platform independent and let it call the platform dependent
Shell::OSExit() at the end.

R=rmcilroy@chromium.org

Change-Id: I14425b6a5c25b757211bc8b9959a9cc8bfa0602c
Reviewed-on: https://chromium-review.googlesource.com/789038Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49659}

... in the same style as the previous CLs for negation and bitwise-not.

R=jarin@chromium.org

Bug: v8:6791
Change-Id: I0aa96a72421e90c8c82a39dd4264fdcf00967504
Reviewed-on: https://chromium-review.googlesource.com/779141
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49658}

Modification of InstanceType enum caused JsonStringifier::Serialize_() function
to consume more stack space (because of a switch statement) in non-optimized
debug build which now causes stack overflow on certain depth of nested objects.
The modification affects neither optimized debug nor release builds.

Change-Id: Ia2925d9abbd1c32c5a4694e14c49b2d0bd119419
Reviewed-on: https://chromium-review.googlesource.com/789074
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49657}

Bug: 
Change-Id: Ie516167f047e48cda47a5dbfb156ea9ae164046c
Reviewed-on: https://chromium-review.googlesource.com/789878Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49656}

1) Make sure we don't enable prototype setup mode for parent class and its prototype
objects.
2) Make sure we create builtins and their prototypes with completed setup mode.
3) Drive-by-fix: setup typed array classes in bootstrapper.cc instead of typedarray.js,
and drop %FunctionSetPrototype().

Bug: v8:7115, v8:5902
Change-Id: I58ac091d85647abc3307bd47baf48e378e3695c5
Reviewed-on: https://chromium-review.googlesource.com/790992
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49655}

Bug: chromium:788539
Change-Id: I75b6ef7e486b578f123747d79f52c9eb45a0370e
Reviewed-on: https://chromium-review.googlesource.com/792050Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49654}

R=adamk@chromium.org

Bug: chromium:787698
Change-Id: I873debe61b152a9e88ce22d95a69f27eab2d0f55
Reviewed-on: https://chromium-review.googlesource.com/787473Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49653}

This extends the typing rule for NumberTrunc to deal with general number
inputs properly, thus addressing a long-standing TODO. We also add test
cases to ensure that the typing rule gets the corner cases for NaN and
-0 right.

Bug: v8:5267, v8:7109
Change-Id: Iedc541a0f4619f37da37ea36940f92472034cdf2
Reviewed-on: https://chromium-review.googlesource.com/792932Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49652}

This extends the typing rule for NumberRound to deal with general number
inputs properly, thus addressing a long-standing TODO. We also add test
cases to ensure that the typing rule gets the corner cases for NaN and
-0 right.

Bug: v8:5267, v8:7109
Change-Id: Ia865ec1d6f8d96f20641bee96891740a9fc6e627
Reviewed-on: https://chromium-review.googlesource.com/792931Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49651}

This extends the typing rule for NumberCeil to deal with general number
inputs properly, thus addressing a long-standing TODO. We also add test
cases to ensure that the typing rule gets the corner cases for NaN and
-0 right.

Bug: v8:5267, v8:7109
Change-Id: I9154e47e58ad106791613db0030051f2a802a981
Reviewed-on: https://chromium-review.googlesource.com/792930Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49650}

Add/AddSaturateS/Sub/SubSaturateS/AddSaturateU/SubSaturateU
MinS/MaxS/MinU/MaxU
Eq/Ne/GtS/GeS/GtU/GeU

Bug: 
Change-Id: Ib802dcfceac073090602d09a7fb037ec498e493d
Reviewed-on: https://chromium-review.googlesource.com/788595
Commit-Queue: Jing Bao <jing.bao@intel.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49649}

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/75cefe9..cc674b0

Rolling v8/third_party/android_tools: https://chromium.googlesource.com/android_tools/+log/9914c57..a2e9bc7

Rolling v8/third_party/catapult: https://chromium.googlesource.com/catapult/+log/030b060..884db23

Rolling v8/third_party/icu: https://chromium.googlesource.com/chromium/deps/icu/+log/5ed2698..741688e

Rolling v8/third_party/instrumented_libraries: https://chromium.googlesource.com/chromium/src/third_party/instrumented_libraries/+log/ebf8d92..2841745

Rolling v8/tools/clang: https://chromium.googlesource.com/chromium/src/tools/clang/+log/8427dae..8688d26

TBR=machenbach@chromium.org,hablich@chromium.org,sergiyb@chromium.org

Change-Id: I5a9241d5275de50effc511edec163319e6497c03
Reviewed-on: https://chromium-review.googlesource.com/792278Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49648}

This enforces that we use ParseExpressionCoverGrammar, and not ParseExpression,
for several tricky cases. Also clarify comment on ParserBase::ParseExpression().

Change-Id: I1d1289abdf539c96f4b42f97c79a8adf3c06e728
Reviewed-on: https://chromium-review.googlesource.com/783171
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49647}

Besides avoiding the weird hack of inserting a statement at the 0th
index of the function body, we also avoid allocating (and initializing)
the variable if it's unreferenced (which I'd wager is the common case).

Bug: v8:6092
Change-Id: If917d422bb4818cf21e8272aa786ca84d4472802
Reviewed-on: https://chromium-review.googlesource.com/784092Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49646}

Bug: v8:6092
Change-Id: I518516d3600458faba5ace1eee1e5b5c3cc560ce
Reviewed-on: https://chromium-review.googlesource.com/784127Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49645}

Align Push/PopCallerSaved register list, and remove unused options for two and
three exclusion registers.

Bug: v8:6644
Change-Id: I70df24837b09402e32ddc2a25a3061cd61ec0301
Reviewed-on: https://chromium-review.googlesource.com/790290Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Martyn Capewell <martyn.capewell@arm.com>
Cr-Commit-Position: refs/heads/master@{#49644}

Pull most JSTypedArray source arguments onto the fast path.

Same source & target elements-kinds simply call memmove. Other
combinations call directly into C and reuse ElementsAccessor logic.

Only overlapping source & target args with differing elements-kinds
remain on the slow runtime path.

Bug: v8:7123, v8:3590
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: I80284b61478b0e3266b8f16bde8a56bd90f080b0
Reviewed-on: https://chromium-review.googlesource.com/788857
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49643}

Introduce new runtime flag that forces to always use
slow path for regex, promise and array builtins. It
works in DEBUG or with new compile time flag
ENABLE_FASTSLOW_SWITCH.

It will be used in the fast/slow path fuzzer or as a
testing variant to ensure that slow path implementation
behave equivalent to corresponding fast paths (where
applicable).

Bug: v8:7120
Change-Id: Ia2a4ab7aca5051e852723782c529bd2e8e5925ca
Reviewed-on: https://chromium-review.googlesource.com/787291
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49642}