Cancel resources in the plugin process when a user presses the stop button or window.stop() is called.

BUG=286074
R=ananta@chromium.org

Review URL: https://codereview.chromium.org/24302012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225099 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225099