Original change's description:
> Switch tracing to use v8::TracingController
>
> BUG=v8:6511
> R=fmeawad@chromium.org
>
> Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> Change-Id: I4961e4b61a9ddc98385ed97c3ffcbcaef2d9cba7
> Reviewed-on: https://chromium-review.googlesource.com/543144
> Commit-Queue: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: Fadi Meawad <fmeawad@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46307}

BUG=v8:6511
TBR=fmeawad@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng;master.tryserver.v8:v8_linux64_tsan_rel
Change-Id: Ide32b409248dfd466e7c0bae1d8ae61d6a955d98
Reviewed-on: https://chromium-review.googlesource.com/558865
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46381}

This reverts commit 3d8e87aa.

Reason for revert: tsan errors:
https://build.chromium.org/p/client.v8/builders/V8%20Linux64%20TSAN/builds/15977

Original change's description:
> Switch tracing to use v8::TracingController
> 
> BUG=v8:6511
> R=​fmeawad@chromium.org
> 
> Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
> Change-Id: I4961e4b61a9ddc98385ed97c3ffcbcaef2d9cba7
> Reviewed-on: https://chromium-review.googlesource.com/543144
> Commit-Queue: Jochen Eisinger <jochen@chromium.org>
> Reviewed-by: Fadi Meawad <fmeawad@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46307}

TBR=fmeawad@chromium.org,jochen@chromium.org

Change-Id: I3f39081001104c634cc8cab9d58ec420fc7293d8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6511
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/554771Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46308}

BUG=v8:6511
R=fmeawad@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I4961e4b61a9ddc98385ed97c3ffcbcaef2d9cba7
Reviewed-on: https://chromium-review.googlesource.com/543144
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Fadi Meawad <fmeawad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46307}

In the lightweight mode it only maintains pseudo stack and does not
collect timing information. It can be used in the sampling mode.

BUG=chromium:660428

Review-Url: https://codereview.chromium.org/2472193002
Cr-Commit-Position: refs/heads/master@{#40812}

This patch removes TracingCategoryObserver API and moves the creation of
observer inside platform initialization, by assuming that either
Platform::AddTraceStateObserver is implemented correctly to add observer to
tracing controller that implemented by embedders, or default tracing controller
has already been set up and attached to platform before
v8::V8::InitializePlatform is called.

BUG=v8:5590

Review-Url: https://codereview.chromium.org/2471583004
Cr-Commit-Position: refs/heads/master@{#40739}

This patch implements TracingCategoryObserver to set global flag when a V8
specific category is enabled. Previously, we set a global flag each time when we
encounter a top level trace event, and use it as a global check. With this
patch, we can set a group of flags when tracing is enabled; besides, we make
V8 tracing feature use V8 flags instead of defining its own flag in a messy way.

With this patch, whatever V8 flag we want to imply in tracing, we define another
integer flag, and the original V8 flag will set it to 0x01 when passing by
commandline, tracing will set it to 0x10 when we start tracing and reset the bit
when we stop tracing.

Review-Url: https://codereview.chromium.org/2436273002
Cr-Commit-Position: refs/heads/master@{#40659}