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After crrev.com/1117423002 VideoFrames can carry three textures, each
one representing a different YUV plane.
VideResourceUpdater needs to create a YUV external resource in case the
VideoFrame contains three native texture representing a frame in YUV420.

BUG=485859

Review URL: https://codereview.chromium.org/1127423006

Cr-Commit-Position: refs/heads/master@{#329290}