Fix crash when a Frame gets reparented from one RenderView to another because of adoptNode. The problem was that the UserScriptIdleScheduler was relying on the FrameDetached notification from its _original_ RenderView, to know when it should delete itself since the frame_ object was gone. But when the frame gets reparented, the FrameDetached only gets sent to observers of the _new_ RenderView.

      The fix is to have ExtensionHelper, which is per-RenderView, proxy all these calls to ExtensionHelper, which is per-renderer.  ExtensionHelper then keeps the map of WebFrame->UserScriptIdleSchedulers, and notifies them of these events.

BUG=78516
Review URL: http://codereview.chromium.org/6814004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80988 0039d316-1c4b-4281-b951-d872f2087c98