If a page is navigated within the same render process, the active notifications need to go out of scope so we don't try to fire events on them back to the original page.

      BUG=32862
TEST=reload page then close notification

Review URL: http://codereview.chromium.org/549140

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@37019 0039d316-1c4b-4281-b951-d872f2087c98