[Cross-Site Isolation] Migrate entire MediaStream verticals to be per-RenderFrame.

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 ac836bb809b3dd0f8d2eee93c487bea0b3e59681..d298065e40bb5fe65e9fbde68a40f5f863c2dbcf 100644
--- a/content/public/renderer/render_frame_observer.h
+++ b/content/public/renderer/render_frame_observer.h
@@ -54,6 +54,10 @@ class CONTENT_EXPORT RenderFrameObserver : public IPC::Listener,
   virtual void DidClearWindowObject() {}
   virtual void DidChangeName(const base::string16& name) {}
 
+  // Called when the frame will soon be closed. This is the last opportunity to
+  // send messages to the host (e.g., for clean-up, shutdown, etc.).
+  virtual void FrameWillClose() {}
+
   // Called when we receive a console message from Blink for which we requested
   // extra details (like the stack trace). |message| is the error message,
   // |source| is the Blink-reported source of the error (either external or