Convert remaining WebContentsObservers loading callbacks to use RFH.
Fix several WebContentsObserver implementations that are incorrectly
caching only frame routing IDs in order to act only on that frame in
later callbacks. Frame routing IDs by themselves are not suitable for
identity comparisons, since they are only unique within a given
RenderProcessHost.
Also clean up WebContentsObservers with a redundant WebContents
field. By definition, a WebContentsObserver must know which
WebContents it's observing, so there's no need for derived classes
to maintain their own WebContents field.
BUG=none
Review URL: https://codereview.chromium.org/
373623002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282043 0039d316-1c4b-4281-b951-d872f2087c98