[DevTools] Add Notifications & Push Messaging views.

Add basic UI for Notifications & Push Messaging in Application >
Background Services.
One UI flag per feature is created.

TBR=caseq@chromium.org

Screenshot: crbug.com/942174#c28
Bug: 942174
Change-Id: Ifcdca9d3d78593968b0bd93d02d9dfea9419b822
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611612
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661384}
4 files changed