The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/336743c75471ed1036037c0c423a78b4ad41fe3f

commit 336743c75471ed1036037c0c423a78b4ad41fe3f
Author: xidachen <xidachen@chromium.org>
Date: Tue Nov 22 01:06:13 2016

Correct the OffscreenCanvas.getContext API

Currently this API takes a DOMString as its first argument. The spec
recently changed to let it take an enum as the first argument. This CL
makes the change and adds a test case.

This CL also makes OffscreenCanvas support webgl2 context creation. To test that, there is a github pull request here:
https://github.com/KhronosGroup/WebGL/pull/2159
Locally it works fine.

BUG= 666024 ,  666339 
TBR=haraken@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2509193002
Cr-Commit-Position: refs/heads/master@{#433721}

[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/LayoutTests/fast/canvas/OffscreenCanvas-getContext.html
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/ModulesInitializer.cpp
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.idl
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.cpp
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContext.h
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp
[modify] https://crrev.com/336743c75471ed1036037c0c423a78b4ad41fe3f/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.h