[Mac] Prevent inactive pinned tabs from throbbing continuously when media indicator is on.

This was caused by TabStripController::setTabTitle() being called repeatedly (i.e., several times per second) while audio is playing.  From there, TabController::setTitle() was being called repeatedly; and, therefore, the alert throbber animation was being repeatedly restarted.

The short-term solution is to put in a simple check to determine whether the title text has actually changed; and, if not, don't do anything.  In the long term, we need to do a larger clean-up of the Mac tab strip UI to eliminate redundant processing.

BUG=323042
R=avi@chromium.org

Review URL: https://codereview.chromium.org/106983006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239596 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239596