Fixing compositing of layers with rounded corners or clip-paths

This change prevent bounds-based occlusion optimizations with
occluding layers that have a clip path or rounded corners.

BUG=311579

Review URL: https://codereview.chromium.org/50413013

git-svn-id: svn://svn.chromium.org/blink/trunk@161273 bbb929c8-8fbe-4397-9dbb-9b2b20218538