Apply clips to cc layer hit test rects

It is very common that iframes get clipped by a container on the
web. We previously marked any clipped iframes to require the slow path.

This CL checks if all transforms applied to an iframe preserve
isothetic alignment so that we can use a single accumulated clip
region as the hit test rect.

Bug: 825817
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ide233736b1cd375bc1b96172a3fa4cba5afc9a42
Reviewed-on: https://chromium-review.googlesource.com/1000135
Commit-Queue: Xianda Sun <sunxd@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578338}
16 files changed