Skip clip rect computation when layer and its target are unclipped.

This also removes a bug where a clip child was using the entire clip of
its clip parent's target while computing its visible rect, it now uses
only the local clip of the clip parent.

BUG=537797
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1390403003

Cr-Commit-Position: refs/heads/master@{#353191}
5 files changed