See GL_EXT_texture_format_BGRA8888.

TRAC #22410
Signed-off-by: Geoff Lang
Signed-off-by: Daniel Koch
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/dx11proto@1771 736b8ea6-26fd-11df-bfd4-992fa37f6226