[Mac] Redesign of the avatar menu button.
- Made the (old) avatar icon badge be a subclass of the (future, new in this CL)
avatar button, and moved the common code (opening the avatar bubble, listening to profile changes) up in the parent class.
- Made this class use a ProfileInfoCacheObserver rather than the NotificationService
- Added unit tests for the new code 
- Small change in c/b/ui/views/frame/browser_view.cc to re-use a new 
method in profiles_state.cc that checks whether a profile is a normal/guest 
mode profile (i.e. not incognito)

Screenshots: https://drive.google.com/folderview?id=0B1B1Up4p2NRMUW5zeFp6MkY5UDA&usp=sharing

This is behind the --new-profile-management flag, and shows the avatar
switcher as a menu button in the caption area. The button shows the user's
name, rather than an image.

BUG=324036
TEST=With the --new-profile-management flag on, start Chrome. Whether 
you have one user or more, you should see a button in the top right corner of 
the browser displaying the active profile's name. The guest browser should 
display "Guest", and the button should work otherwise as the existing avatar 
icon. In incognito mode, the spy dude icon should be displayed as before.

Review URL: https://codereview.chromium.org/117533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246700 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246700