Added code to call CloseAsh in place of closing secondary widgets on Windows.
Here is what happens in attached bug:
1. UserManagerView (Profile view) adds a reference to browser process by calling StartKeepAlive.
2. UserManagerView is a secondary widget.
3. Current code for windows does EnumWindows for closing all secondary widgets in CloseAllSecondaryWidgets, which works only for desktop mode.
4. In Chrome on ASH EnumWindows doesn't do anything as they are not regular windows.
5. Because UserManagerView doesn't get chance to close through CloseAllSecondaryWidgets, it doesn't release reference and we browser process keeps running.

CloseAsh closes all child widgets, which might be a overkill but works for now.

BUG=340967
R=sky@chromium.org, ananta, cpu, sky

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=256244

Review URL: https://codereview.chromium.org/173403002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256370 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256370