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This CL adds MediaOzonePlatform, a new Ozone component for abstracting media
and related. In particular it adds CreateVideoDecodeAccelerator method so Ozone
implementations can use that for abstracting video decoding acceleration (i.e.
GPU based video decoding). Eventually MediaOzonePlatform will be used as well
for many windowing systems abstractions related to media, e.g. video encode,
audio, etc. We will add support for these others as needed.

Media platform is called and created on demand whenever a video playback is set
to play. Different than ui::OzonePlatform methods, the one added in here is 
non-pure virtual so the implementations can decide themselves whether a video 
implementation is actually wanted, based on its hardware capabilities.

This work is aimed at internal implementations like Ozone-DRI, Ozone-test but
also for externals like Ozone-Wayland. Different targets like Chromium Browser,
Chrome OS, ChromeCast and others can now take advantage of it.

BUG=380884
TEST=manually on Ozone-Wayland, using:

 $ export GYP_DEFINES='chromeos=0 use_ozone=1 proprietary_codecs=1 ffmpeg_branding=Chrome'
 $ ninja -j16 -C out/Release content

and to run:

 ~/git/chromium/src/out/Debug$ ./chrome --no-sandbox --user-data-dir=/tmp/chrome --ignore-gpu-blacklist ../../third_party/WebKit/PerformanceTests/resources/bear-1280x720.mp4  --vmodule=*/ozone/ui*=3 --v=0

additionally, in Release builds you can start chrome with --disable-accelerated-video-decode to compare the results.

Review URL: https://codereview.chromium.org/269673005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276552 0039d316-1c4b-4281-b951-d872f2087c98