Support frame tree propagation between renderers in the same browsing instance.

content/browser/renderer_host/render_view_host_delegate.h

Index: content/browser/renderer_host/render_view_host_delegate.h
diff --git a/content/browser/renderer_host/render_view_host_delegate.h b/content/browser/renderer_host/render_view_host_delegate.h
index bfbac694a33c2af399ee5f670bc87b0bfa843729..c14fc788b49a437a435971a4504d55e7281c1f49 100644
--- a/content/browser/renderer_host/render_view_host_delegate.h
+++ b/content/browser/renderer_host/render_view_host_delegate.h
@@ -215,6 +215,10 @@ class CONTENT_EXPORT RenderViewHostDelegate {
   // entirely loaded).
   virtual void DidChangeLoadProgress(double progress) {}
 
+  // The RenderView has changed its frame hierarchy, so we need to update all
+  // other renderers interested in this event.
+  virtual void DidUpdateFrameTree(RenderViewHost* rvh) {}
+
   // The RenderView's main frame document element is ready. This happens when
   // the document has finished parsing.
   virtual void DocumentAvailableInMainFrame(RenderViewHost* render_view_host) {}