Add CHROMIUM_ycbcr_422_image extension.
Add an extension that provides a method for GL to process images that
are defined in '2vuy' video format.
GL_YCRCR_422_CHROMIUM <internalformat> as been added and it is an accepted
value when creating an image if the extension is supported.
This extension maps to GL_APPLE_ycbcr_422 and will allow us to determine if
we can use IOSurfaces with that format.
BUG=524582
Review URL: https://codereview.chromium.org/
1305153005
Cr-Commit-Position: refs/heads/master@{#345693}