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