Ensure all subviews of NotifierButton are released properly.

The image view for the icon is sometimes not freed when the icon is
never added to the view hierarchy.  This change transfers ownership
to the button instead of views.

NOTRY=true
TBR=mukai@chromium.org
BUG=314392

Review URL: https://codereview.chromium.org/57083002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232643 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232643