Add check for window on view in MouseObserver
Add check for window on view in MouseObserver

BUG=chromium-os:12119
TEST=None

Review URL: http://codereview.chromium.org/6612039

git-svn-id: http://src.chromium.org/svn/trunk/src@77492 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: b9628908a838eee2836b903daed8e8cfd0321799
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser