Remove ChromeRenderViewHostObserver as part of removing RenderViewHostObserver.

-the extension code in RenderViewHostInitialized maps directly to WebContentsObserver::RenderViewCreated.
-RenderViewHostObserver::RenderViewHostDestroyed maps directly to WebContentsObserver::RenderViewDeleted
-the predictor code in RenderViewHostObserver::Navigate maps directly to WebContentsObserver::NavigateToPendingEntry
-the dispatched IPCs were moved to the CoreTabHelper WebContentsObserver

The only difference is that the constructor also used to call InitRenderViewForExtensions. However the code said that that method is called in RenderViewHostInitialized to handle the tab-crash scenario, so that means by definition that that method is also sufficient for initial RVH creation.

BUG=306569
R=mpcomplete@chromium.org

Review URL: https://codereview.chromium.org/26538011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228997 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228997