Make blit extension check for internal format mismatch. The extension spec dictates a format mismatch generates invalid operation. Since we can't have the same internal format map to different actual/native formats, this check is more strict and we can replace the previous one. BUG=angle:769 Change-Id: Ic1b5c335ba38a4f2feaffa1478a65e7fcf7f75ea Reviewed-on: https://chromium-review.googlesource.com/221065 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>