cc: Split IsClippedCorrectly unit test into two versions

cc: Split IsClippedCorrectly unit test into two versions

The main thread doesn't know anything about render surface clipping.
However, the main thread is the only place that sets is_clipped on
layers, so it seemed worthwhile keeping both versions of this test, even
if it's a bit redundant.

It's possible that is_clipped can be answered by property trees instead
of layer properties in the future, in which case this could be collapsed
back into one test.

R=weiliangc@chromium.org,ajuma@chromium.org
BUG=502041
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1300723003

Cr-Commit-Position: refs/heads/master@{#343959}