GitLab

This CL adds a test helper header platform/testing/PaintPropertyTestHelpers.h
for common operations that are used in SPv2-related tests.

createOpacityOnlyEffect is added to create effect nodes with only opacity,
other optional effects are assigned a no-op value, and local transform space
and clip are inherited from parent.

As a side change, rootPaintChunkProperties is also moved to the helper header
and renamed to defaultPaintChunkProperties.
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2565903002
Cr-Commit-Position: refs/heads/master@{#437994}