Merge VideoDecodeAcceleratorImpl with VideoDecodeAccelerator

This moves the single method CanDecodeOnIOThread on
VideoDecodeAcceleratorImpl to VideoDecodeAccelerator. The
implementations that were subclasses of VideoDecodeAcceleratorImpl now
get an override for CanDecodeOnIOThread that returns false.

TEST=linux desktop build
BUG=380884

Review URL: https://codereview.chromium.org/317083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275621 0039d316-1c4b-4281-b951-d872f2087c98
14 files changed