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
Fix GenericEventQueue tracing for cancelled events.

Events that were cancelled via clearAllEvents() did not have trace
events associated with them so these events would look like they went
on forever in the tracing visualization. This change provides the
proper trace event to prevent this.

Review URL: https://codereview.chromium.org/45463005

git-svn-id: svn://svn.chromium.org/blink/trunk@161274 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add an Error class for ServiceWorkers

This class could eventually be generically exposed as WebError, and wrap DOMError.

BUG=285976

Review URL: https://codereview.chromium.org/27278002

git-svn-id: svn://svn.chromium.org/blink/trunk@161275 bbb929c8-8fbe-4397-9dbb-9b2b20218538