Move handling of DraggableRegionsChanged notification from "view" to "frame".

content/public/renderer/render_frame_observer.h

Index: content/public/renderer/render_frame_observer.h
diff --git a/content/public/renderer/render_frame_observer.h b/content/public/renderer/render_frame_observer.h
index ebf4cd4b118cacb9469547ee83788834f6dd55db..8bb72a3a7abbd72893d3f6121be75ab1ce025c39 100644
--- a/content/public/renderer/render_frame_observer.h
+++ b/content/public/renderer/render_frame_observer.h
@@ -124,6 +124,9 @@ class CONTENT_EXPORT RenderFrameObserver : public IPC::Listener,
   // Called when script in the page calls window.print().
   virtual void ScriptedPrint(bool user_initiated) {}
 
+  // Called when draggable regions change.
+  virtual void DraggableRegionsChanged() {}

[dcheng, 2017/06/09 22:21:54]

I wonder if it's worth noting this is main frame only.

[Łukasz Anforowicz, 2017/06/13 18:24:10]

Maybe.  We talked about this today and this sounds like something that we might
want to consider outside of this CL.

If we do want to note that some notifications (DraggableRegionsChanged,
DidChangeIcon) are (or can be) for main-frame only, then what options do we
have?

1) comments + DCHECKs?

2) WebMainFrameClient (a subclass of WebFrameClient)?

3) Some other option?

Also - how many notifications are we talking about?  You mentioned that in
addition to DraggableRegionsChanged and DidChangeIcon there was also something
about manifests - maybe you meant DidChangeManifest?  Are there other such
notifications?  Are there some non-notification things that are main-frame-only
and that don't belong in Page and/or WebView (and being non-notifications
probably don't belong in Web[Main]FrameClient)?

+
   // IPC::Listener implementation.
   bool OnMessageReceived(const IPC::Message& message) override;