GitLab

This CL makes several improvements to the accessibility of the intent
picker bubble:

1. Reducing the opacity applied to the ink drop highlight for focused
   items (increasing text contrast slightly)
2. Adding a role override to the bubble to avoid the screen reader
   saying "Unknown" for the picker purpose
3. Making each label button focusable so they can be tabbed through.

BUG=760200,825700

Change-Id: Ib2477b786350b07325a615f77ba4b168b1bb5cc7
Reviewed-on: https://chromium-review.googlesource.com/1102228
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Reviewed-by: David Jacobo <djacobo@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568234}