Revert "Remove notifications from TabStripModel."

This reverts r228620.

BUG=170921, 309557
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/38023003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230718 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230718