TEST=conformance/extensions/webgl-compressed-texture-s3tc-srgb
BUG=angleproject:2049

Change-Id: I00d816299db914c078d140f791cd7c98c6428a54
Reviewed-on: https://chromium-review.googlesource.com/522762Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>