events: Update EventTargeter to operate on the EventTarget that owns the targeter.

BUG=318879
R=ben@chromium.org

Review URL: https://codereview.chromium.org/98353008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243118 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243118