Canvas: Improve CanvasResourceDispatcherTest

This CL adds a new test case to CanvasResourceDispatcherTest, generating
a CompositorFrame and inspecting its contents, specially regarding its
expected opacity, size and |damage_rect|.

For that, it moves the Mock classes landed in crrev.com/c/1228859 to
one level deeper renderer/platform/graphics/test/ so it can be used
from where CanvasResourceDispatcherTest lives.  At the same time, it
extracts the hardcoded ASSERT/EXPECT out of it, to be run in the test
cases themselves and finally renames the file to mock_compositor_frame_sink
to better reflect what it does now.

This CL only touches webkit_unit_tests stuff.

Bug: 788439
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6af472f0cc6e80c17bd707f0734ad83a4688d021
Reviewed-on: https://chromium-review.googlesource.com/1238798
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593454}
8 files changed