Fix: tabs slow to response to beforeunload are closed prematurely.

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 383 matching lines @@
   // canceled or suspended. This is important if we later return to this
   // RenderFrameHost.
   void CancelSuspendedNavigations();
 
   // Runs the beforeunload handler for this frame. |for_navigation| indicates
   // whether this call is for the current frame during a cross-process
   // navigation. False means we're closing the entire tab.
   // PlzNavigate: this call happens on all browser-initiated navigations.
   void DispatchBeforeUnload(bool for_navigation);
 
+  // Next |DispatchBeforeUnload| will be treated as a new event even if
+  // frame hasn't responded with |OnBeforeUnloadACK| yet.
+  void DontWaitForBeforeUnloadAck();
+
   // 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();
 
   // 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();
 
@@ skipping 559 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_