[EoC] A toolbar entry point behind a new flag

Add an experimental toolbar button that triggers the contextual
suggestions bottom sheet.

Currently the auto-peek behavior for the contextual suggestions bottom
sheet is not disabled when the toolbar button is enabled. This will be
handled in a follow-up CL.

BUG=856403

Change-Id: Ic56aeb44f8ce9dc29606a902553d9d25803df40e
Reviewed-on: https://chromium-review.googlesource.com/1115352
Commit-Queue: Theresa <[email protected]>
Reviewed-by: Ted Choc <[email protected]>
Reviewed-by: Matthew Jones <[email protected]>
Reviewed-by: Filip Gorski <[email protected]>
Cr-Commit-Position: refs/heads/master@{#570954}
25 files changed