Introduce RenderFrame::IsMainFrame and clean up a few things.

content/public/renderer/render_frame.h

Index: content/public/renderer/render_frame.h
diff --git a/content/public/renderer/render_frame.h b/content/public/renderer/render_frame.h
index 4bb763bbeb06fda3974c6d5a101b80ce8323db33..335c2234416af8ce9cc851c4274ef07eea26b823 100644
--- a/content/public/renderer/render_frame.h
+++ b/content/public/renderer/render_frame.h
@@ -115,6 +115,9 @@ class CONTENT_EXPORT RenderFrame : public IPC::Listener,
   // Execute a string of JavaScript in this frame's context.
   virtual void ExecuteJavaScript(const base::string16& javascript) = 0;
 
+  // Returns true if this is the main (top-level) frame.
+  virtual bool IsMainFrame() = 0;
+
   // Return true if this frame is hidden.
   virtual bool IsHidden() = 0;