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VideoFrame can carry YUV native textures.
After crrev.com/1127423006 VideoResoucesUpdater will create the
appropriate VideoFrameExternalResources.
This change makes VideoLayerImpl deal with a VideoFrame with a
NATIVE_TEXTURE format and a TEXTURE_YUV_420 texture format.

BUG=485859

Review URL: https://codereview.chromium.org/1125303005

Cr-Commit-Position: refs/heads/master@{#330017}