Set Event.composed flag correctly for some of UA UIEvents

See https://github.com/w3c/webcomponents/issues/513 for the context.

See also the previous CL: https://codereview.chromium.org/2012423004, where
Event.composed was introduced.

The change is visible only when Shadow DOM v1 is used.

BUG=531990,616654

Review-Url: https://codereview.chromium.org/2030243004
Cr-Commit-Position: refs/heads/master@{#397681}
12 files changed