Disable dynamic pixel shader generation. Always generate the same pixel shader no matter what framebuffer is bound. BUG=angle:670 Change-Id: I3fa91ff43363d49b38a19d3815ea523946c675d5 Reviewed-on: https://chromium-review.googlesource.com/204573 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>