Upstream WebAPK notification related code

This CL makes Chrome hand off displaying notifications which fall within the
URL scope of a WebAPK to the WebAPK. Doing the hand off enables these
notifications to look in the Android UI as if they were dispatched by the WebAPK
- not Chrome.

BUG=609122

Review-Url: https://codereview.chromium.org/1969303002
Cr-Commit-Position: refs/heads/master@{#395157}
20 files changed