https://codereview.chromium.org/2518623004 implements this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b368c8ec4a79496fb2816aa79d3e5c235a4843c4

commit b368c8ec4a79496fb2816aa79d3e5c235a4843c4
Author: kbr <kbr@chromium.org>
Date: Mon Nov 21 17:10:03 2016

Removed leftover enums from WebGL 2.0 rendering context.

Also includes needed WebGL conformance roll:

Roll WebGL 453428f..d12037a

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/453428f..d12037a

BUG= 666927 
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/2518623004
Cr-Commit-Position: refs/heads/master@{#433573}

[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/DEPS
[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/third_party/WebKit/LayoutTests/platform/linux/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/third_party/WebKit/LayoutTests/platform/win/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/third_party/WebKit/LayoutTests/virtual/stable/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/b368c8ec4a79496fb2816aa79d3e5c235a4843c4/third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.idl

Requesting merge to M56. While this change is small and not functionally significant, it's needed in order to pass the WebGL 2.0 conformance tests -- which Chrome needs to do in order to enable the functionality, by our working group's own rules.

[Automated comment] DEPS changes referenced in bugdroid comments, needs manual review.

Merge approved for M56 branch 2924.  Please be aware that updating DEPS differs between trunk and branch (e.g. just cherry-picking the change in c#4 would leave things in a broken state).  If you're unfamiliar with changing branch DEPS ping me and I can point you in the right direction.

This was merged to branch 2924 in https://codereview.chromium.org/2521323004 and the associated WebGL conformance roll was landed in https://chromereviews.googleplex.com/544427013 . Not sure why the first CL didn't generate the appropriate email, but adding the correct labels.