First draft of an App Service ARC++ publisher

Lots of TODOs, but there's enough implemented so that running "chrome
--enable-features=AppService" will populate the launcher with ARC++
apps' names and icons, and clicking on the icon will launch the app.

BUG=826982

Change-Id: Ie61b33ce9fa0588e53615f5e086d558fe6abf840
Reviewed-on: https://chromium-review.googlesource.com/c/1377485
Commit-Queue: Nigel Tao <[email protected]>
Reviewed-by: Dominick Ng <[email protected]>
Reviewed-by: James Cook <[email protected]>
Cr-Commit-Position: refs/heads/master@{#621923}
12 files changed