Merge to M46 for BUG=510252

Merge to M46 for BUG=510252
Re-land: Enable GpuMemoryBuffers video frames on MacOS.

This patch enables UYVY GpuMemoryBuffers backed VideoFrames on MacOSX
for software decoded videos.
This change allows VideoLayers to be promoted to overlays when possible.
Power measurements showed a significant reduction in Watts consumed
during video playback: in the tests ran by ccameron@ it went from 3.15
Watts to 2.13 Watts.

Additionally this change avoids one copy of the VideoFrame in the GPU
process and moves away another copy from the Compositor thread to
media.

Unfortunately, for videos where the decoding time is close to the frame
time, the additional copy might slow down the decoding past the limit,
causing more dropped frames in these cases.

More benchmark results can be found here:
https://x20web.corp.google.com/~dcastagna/results_all.html

The first run is with GMB video frames disabled, the second one, enabled.

BUG=485859, 510252
Committed: https://crrev.com/96463459619f441a721f96c51c357208604b7475
Cr-Commit-Position: refs/heads/master@{#345418}

Review URL: https://codereview.chromium.org/1308913003

Cr-Commit-Position: refs/heads/master@{#347566}
(cherry picked from commit b65e607913fe32132494e877bc1b70108e4d0e20)

BUG=510252
Committed: https://chromium.googlesource.com/chromium/src/+/1357e461dc5b2cff3c0db798bf15a918701964e3

[ccameron, 2015-09-14 17:34:33]

Committed patchset #1 (id:1) manually as
1357e461dc5b2cff3c0db798bf15a918701964e3.