Implement CHROMIUM_copy_texture for OpenGL. This also makes BlitGL work correctly on OpenGL ES (provided vertex arrays are available) BUG=angleproject:1356 Change-Id: Icb7cef35bebfe6672220aa0b312ab89187dbf585 Reviewed-on: https://chromium-review.googlesource.com/412452 Commit-Queue: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>