This is a first step towards moving Turbofan code generation off the main thread.

Summary of the changes:
- AssemblerBase no longer has a pointer to the isolate. Instead, its
  constructor receives the few things that it needs from the isolate (on most
  architectures this is just the serializer_enabled flag).
- RelocInfo no longer has a pointer to the isolate. Instead, the functions
  that need it take it as an argument.  (There are currently still a few that
  implicitly access the isolate through a HeapObject.)
- The MacroAssembler now explicitly holds a pointer to the isolate (before, it
  used to get it from the Assembler).
- The jit_cookie also moved from AssemblerBase to the MacroAssemblers, since
  it's not used at all in the Assemblers.
- A few architectures implemented parts of the Assembler with the help
  of a Codepatcher that is based on MacroAssembler.  Since the Assembler no
  longer has the isolate, but the MacroAssembler still needs it, this doesn't
  work anymore.  Instead, these Assemblers now use a new PatchingAssembler.

BUG=v8:6048

Review-Url: https://codereview.chromium.org/2732273003
Cr-Commit-Position: refs/heads/master@{#43890}

From asm.js code we might get an empty ArrayBuffer as heap memory. In
this case, both the old memory start and the new memory start will be
nullptr. The size however has to be patched from default_size to 0.

This CL changes code specialization to be able to either patch memory
references, or patch memory sizes or both.

R=titzer@chromium.org, ahaas@chromium.org
BUG=chromium:698587

Change-Id: I4d9d811d75cb83842f23df317e8e7fc02aeb5146
Reviewed-on: https://chromium-review.googlesource.com/450257
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43613}

BUG=v8:5294

Change-Id: If45f25aae8de526027b7851cb4efe0ccf4a7c4b1
Reviewed-on: https://chromium-review.googlesource.com/444226
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43388}

 - Refactor Dispatch tables to have separate function, signature tables
 - New Relocation type for WasmFunctionTableReference, assembler, compiler support.
 - RelocInfo helper functions for Wasm references

Review-Url: https://codereview.chromium.org/2627543003
Cr-Commit-Position: refs/heads/master@{#42192}

BUG=v8:5614

Review-Url: https://codereview.chromium.org/2493173002
Cr-Commit-Position: refs/heads/master@{#40916}

Add new relocation type WASM_MEMORY_SIZE_REFERENCE, use relocatable pointers to update wasm memory size references in generated code.
 - Add new RelocInfo mode WASM_MEMORY_SIZE_REFERENCE in the assembler and add relocation information to immediates in compare instructions.
 - Use relocatable constants for MemSize/BoundsCheck in the wasm compiler

R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org

Review-Url: https://codereview.chromium.org/1921203002
Cr-Commit-Position: refs/heads/master@{#36044}

Add relocatable pointers for wasm memory references that need to be updated when wasm GrowMemory is used. Code generator changes to accept relocatable constants as immediates.

R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org

Committed: https://crrev.com/eb5fe0df64ec0add423b2a1f6fb62d5a33dce2a5
Cr-Commit-Position: refs/heads/master@{#35182}

Committed: https://crrev.com/297932a302ce0b73c3618ef9e4eba9d9d241f2b3
Cr-Commit-Position: refs/heads/master@{#35400}

Review URL: https://codereview.chromium.org/1759383003

Cr-Commit-Position: refs/heads/master@{#35407}

Revert of [compiler] Add relocatable pointer constants for wasm memory references. (patchset #15 id:320001 of https://codereview.chromium.org/1759383003/ )

Reason for revert:
[Sheriff] Breaks msan:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/7842

Original issue's description:
> [compiler] Add relocatable pointer constants for wasm memory references.
>
> Add relocatable pointers for wasm memory references that need to be updated when wasm GrowMemory is used. Code generator changes to accept relocatable constants as immediates.
>
> R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org
>
> Committed: https://crrev.com/eb5fe0df64ec0add423b2a1f6fb62d5a33dce2a5
> Cr-Commit-Position: refs/heads/master@{#35182}
>
> Committed: https://crrev.com/297932a302ce0b73c3618ef9e4eba9d9d241f2b3
> Cr-Commit-Position: refs/heads/master@{#35400}

TBR=bradnelson@chromium.org,titzer@chromium.org,bmeurer@chromium.org,bradnelson@google.com,gdeepti@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1881913002

Cr-Commit-Position: refs/heads/master@{#35401}

Add relocatable pointers for wasm memory references that need to be updated when wasm GrowMemory is used. Code generator changes to accept relocatable constants as immediates.

R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org

Committed: https://crrev.com/eb5fe0df64ec0add423b2a1f6fb62d5a33dce2a5
Cr-Commit-Position: refs/heads/master@{#35182}

Review URL: https://codereview.chromium.org/1759383003

Cr-Commit-Position: refs/heads/master@{#35400}

Revert of [compiler] Add relocatable pointer constants for wasm memory references. (patchset #14 id:300001 of https://codereview.chromium.org/1759383003/ )

Reason for revert:
Test failures: https://build.chromium.org/p/client.v8/builders/V8%20Mac64/builds/8046

Original issue's description:
> [compiler] Add relocatable pointer constants for wasm memory references.
>
> Add relocatable pointers for wasm memory references that need to be updated when wasm GrowMemory is used. Code generator changes to accept relocatable constants as immediates.
>
> R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org
>
> Committed: https://crrev.com/eb5fe0df64ec0add423b2a1f6fb62d5a33dce2a5
> Cr-Commit-Position: refs/heads/master@{#35182}

TBR=bradnelson@chromium.org,titzer@chromium.org,gdeepti@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1846083005

Cr-Commit-Position: refs/heads/master@{#35185}

Add relocatable pointers for wasm memory references that need to be updated when wasm GrowMemory is used. Code generator changes to accept relocatable constants as immediates.

R=titzer@chromium.org, yangguo@chromium.org, bradnelson@chromium.org

Review URL: https://codereview.chromium.org/1759383003

Cr-Commit-Position: refs/heads/master@{#35182}