Enable GPU Rasterization on AMD GPUs on Chrome OS

Skia gold tests pass, so allow gpu rasterization

BUG=b:113629885
TEST=Deploy chrome to device, confirm "Rasterization: Hardware
     accelerated" in chrome://gpu

Change-Id: I5917274e28edb2a66a885de9a26517d10952453d
Reviewed-on: https://chromium-review.googlesource.com/c/1374914
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Drew Davenport <ddavenport@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617390}