Adds NULL checks to AeroPeekManager. This change just adds NULL checks to prevent crashes when TabStipModel calls its observers with NULL pointers.
Adds NULL checks to AeroPeekManager.
This change just adds NULL checks to prevent crashes when TabStipModel calls its observers with NULL pointers.

BUG=63854
TEST=launch Chromium with a '--enable-aero-peek-tabs' option.
Review URL: http://codereview.chromium.org/5275004

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@68566 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser