Merge the Image class into ImageD3D. BUG=angle:681 Change-Id: I0c0d41fb3ff9592b08ede58a8c2ec2bd2d94a0b2 Reviewed-on: https://chromium-review.googlesource.com/238470 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Brandon Jones <bajones@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>