Fix overlays on Mac OS when running on Core Profile.
The command buffer service must advertise support for
EXT_texture_format_bgra8888 in order for GLImages to work. I scoured
the spec and extensions and it isn't obvious that this format is
supported, but it works and doesn't generate any GL errors (verified
by regenerating the GL bindings with --generate-dchecks).
Also fixed extensions string displayed in about:gpu when running on
core profile on Mac OS.
BUG=516840
Review URL: https://codereview.chromium.org/
1269163004
Cr-Commit-Position: refs/heads/master@{#342039}