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

content/browser/frame_host/render_frame_host_impl.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_
 #define CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 413 matching lines @@
   void DispatchBeforeUnload(bool for_navigation, bool is_reload);
 
   // Simulate beforeunload ack on behalf of renderer if it's unrenresponsive.
   void SimulateBeforeUnloadAck();
 
   // Returns true if a call to DispatchBeforeUnload will actually send the
   // BeforeUnload IPC. This is the case if the current renderer is live and this
   // 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.
   void UpdateOpener();
 
   // Set this frame as focused in the renderer process.  This supports
   // cross-process window.focus() calls.
   void SetFocusedFrame();
 
   // Continues sequential focus navigation in this frame. |source_proxy|
@@ skipping 312 matching lines @@
       const AccessibilityHostMsg_FindInPageResultParams& params);
   void OnAccessibilityChildFrameHitTestResult(const gfx::Point& point,
                                               int hit_obj_id);
   void OnAccessibilitySnapshotResponse(
       int callback_id,
       const AXContentTreeUpdate& snapshot);
   void OnSmartClipDataExtracted(uint32_t id,
                                 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);
   void OnSerializeAsMHTMLResponse(
       int job_id,
       MhtmlSaveStatus save_status,
       const std::set<std::string>& digests_of_uris_of_serialized_resources,
       base::TimeDelta renderer_main_thread_time);
   void OnSelectionChanged(const base::string16& text,
                           uint32_t offset,
@@ skipping 211 matching lines @@
   // this RFH is the pending RenderFrameHost of a RenderFrameHostManager. There
   // will only ever be one suspended navigation, because RenderFrameHostManager
   // will destroy the pending RenderFrameHost and create a new one if a second
   // navigation occurs.
   // PlzNavigate: unused as navigations are never suspended.
   std::unique_ptr<NavigationParams> suspended_nav_params_;
 
   // 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
   // unload_ack_is_for_cross_site_transition_ indicates whether this is for a
   // cross-site transition or a tab close attempt.
   // TODO(clamy): Remove this boolean and add one more state to the state
   // machine.
   bool is_waiting_for_beforeunload_ack_;
 
   // Valid only when is_waiting_for_beforeunload_ack_ or
@@ skipping 159 matching lines @@
 
   // NOTE: This must be the last member.
   base::WeakPtrFactory<RenderFrameHostImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_