Add right-click user switching tutorial bubble.

This design is based on this mock:


1. Launch chrome and make sure there is more than one available profile.
2. Left-click on the Avatar Button.
3. A tutorial bubble should be displayed informing the user they can
   right-click the button to see other users.
4. Close the bubble without dismissing the tutorial, for example by
   clicking in the content area.
5. Reopening the Avatar Menu should still display the tutorial until it
   is explicitly dismissed (clicking the X or the "Ok, got it!" button)
   or until the user right clicks the button.
6. Once dismissed, the tutorial should never be shown again.

Review URL:

Cr-Commit-Position: refs/heads/master@{#330565}
14 files changed