The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/677d1be0fd445e1c9acd455b84ed0f8fb1984064

commit 677d1be0fd445e1c9acd455b84ed0f8fb1984064
Author: liberato@chromium.org <liberato@chromium.org>
Date: Wed Jan 03 02:44:22 2018

Add runtime feature for MojoVideoDecoder.

Remove the build-time flag for MCVD, and replace it with a runtime
flag media::kMojoVideoDecoder.  When enabled, chrome will consider
using MojoVideoDecoder but not GpuVideoDecoder.

Regardless of the flag, WebRTC can still use the VDAs directly.

that the correct decoder was used.

Bug:  765542 
Test: Manually set feature, tried WebRTC and H264 playback.  Verified
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;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
Change-Id: Ibf4fe584507f7d426a75c53e8fd07033f6c4900e
Reviewed-on: https://chromium-review.googlesource.com/786148
Commit-Queue: Frank Liberato <liberato@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Chris Watkins <watk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526600}
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/base/media_switches.cc
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/base/media_switches.h
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/gpu/BUILD.gn
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/gpu/android/codec_wrapper_unittest.cc
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/media_options.gni
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/mojo/clients/mojo_decoder_factory.cc
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/mojo/services/gpu_mojo_media_client.cc
[modify] https://crrev.com/677d1be0fd445e1c9acd455b84ed0f8fb1984064/media/renderers/default_renderer_factory.cc