Keep track in the browser of which frames have onunload and onbeforeunload handlers.

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index ae2bfccdee8ab421771f1e479b43f6be583a0a0c..fd4505bed45df5077206dbfb11bfc0b37f17be93 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -431,6 +431,10 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // frame is the main frame.
   bool ShouldDispatchBeforeUnload();
 
+  // Returns true if the frame or any of its descendents have an onunload
+  // handler.
+  bool ShouldDispatchUnload();

[nasko, 2017/03/29 23:31:26]

Since there is no dispatching of unload handler happening from the browser side,
let's call that HasUnloadHandler or something similar that indicates that
subframes are consulted too. 

[jam, 2017/03/30 14:53:22]

Done.

+
   // Update the frame's opener in the renderer process in response to the
   // opener being modified (e.g., with window.open or being set to null) in
   // another renderer process.
@@ -763,6 +767,8 @@ class CONTENT_EXPORT RenderFrameHostImpl
                                 base::string16 text,
                                 base::string16 html);
   void OnToggleFullscreen(bool enter_fullscreen);
+  void OnBeforeUnloadHandlersPresent(bool present);
+  void OnUnloadHandlersPresent(bool present);
   void OnDidStartLoading(bool to_different_document);
   void OnDidStopLoading();
   void OnDidChangeLoadProgress(double load_progress);
@@ -994,6 +1000,10 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // When the last BeforeUnload message was sent.
   base::TimeTicks send_before_unload_start_time_;
 
+  // Used to track whether the frame has onbeforeunload and onunload handlers
+  bool has_beforeunload_handlers_;
+  bool has_unload_handlers_;
+
   // Set to true when there is a pending FrameMsg_BeforeUnload message.  This
   // ensures we don't spam the renderer with multiple beforeunload requests.
   // When either this value or IsWaitingForUnloadACK is true, the value of