Support GL_ETC1_RGB8_OES in the OpenGL renderer. Passes all dEQP tests related to etc1. Change-Id: I3ab2d51b7664cb2411fdc3247ff65a9e3258185a Reviewed-on: https://chromium-review.googlesource.com/299340 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>