Allow RED internal format for CopyTextureCHROMIUM.

In crrev.com/1434453008 we changed the internal format for images
from R8 to RED but we forgot to change glCopyTextureCHROMIUM internal
format validation.

This breaks video to WebGL on GL Core Profile since APPLE_ycbcr_422 is
not avaiable, we fall back to three R8 planes, and we then fail to validate
RED as internal format.

BUG=587158
CQ_INCLUDE_TRYBOTS=tryserver.chromium.win:win_optional_gpu_tests_rel

Review URL: https://codereview.chromium.org/1703153002

Cr-Commit-Position: refs/heads/master@{#376026}