Create a message filter for message port and worker messages. This allows a nice cleanup of getting rid of the notifications when RenderMessageFilter and WorkerProcessHost go away. SafeBrowsingResourceHandler doesn't need it anymore as well, since it now overrides OnRequestClosed() which does the same thing.

      Review URL: http://codereview.chromium.org/6055002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@69862 0039d316-1c4b-4281-b951-d872f2087c98