Deleting foreign session locally now posts a notification.
* SessionModelAssocaitor DeleteForeignSession now posts session
  dissabled notification
* Added test for this notification.

BUG=300163

Review URL: https://codereview.chromium.org/25195002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226696 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226696