Close crashed incognito-mode app's shell window.

ExtensionService is shared between off-the-record and original profiles
(see ExtensionSystemImpl) and notifies unload events always from
the original profile. ShellWindow should therefore observe the original profile as well.

BUG=281675

Review URL: https://codereview.chromium.org/138843006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247976 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247976