1st step to implement notification panel for chromeos

      - re-using views implementation, but removed layout related code
 - add NotificationPanel
 - added SetSize in BalloonViewHost. I needed this because I removed animation code and NativeViewHostGtk doesn't know about render view. I need to think a bit more to find out how to deal wit this.
 It's using existing balloon collection, but we may need one for chromeos (or may not).

BUG=33306
TEST=none

Review URL: http://codereview.chromium.org/572018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@38255 0039d316-1c4b-4281-b951-d872f2087c98