GitLab

This is the first CL for integrating context menus to App Service.
There will be follow up for this CL to add more menus to App Service:
1. Add Radio menu items
2. Add sub menu.
3. Add menu items for Crostini.
4. Add menu items for ARC apps.
5. Add menu items for Chrome apps/extension apps.
6. Add menu items for Web apps.

BUG=1038487

Change-Id: I933bb680f0f5356eb4675f648664b6280f340c22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999895
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731878}