Don't wait to close tabs waiting for JavaScript dialogs.

content/browser/renderer_host/render_widget_host_impl.h

 // Copyright (c) 2012 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_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 283 matching lines @@
   // the new one will only fire if it has a shorter delay than the time
   // left on the existing timeouts.
   void StartHangMonitorTimeout(
       base::TimeDelta delay,
       RenderWidgetHostDelegate::RendererUnresponsiveType hang_monitor_reason);
 
   // Stops all existing hang monitor timeouts and assumes the renderer is
   // responsive.
   void StopHangMonitorTimeout();
 
+  // Marks the renderer as being known-unresponsive, so that the hang monitor
+  // doesn't wait for responses.
+  void SetHangMonitorKnownUnresponsive(bool unresponsive);
+
   // Starts the rendering timeout, which will clear displayed graphics if
   // a new compositor frame is not received before it expires.
   void StartNewContentRenderingTimeout();
 
   // Notification that a new compositor frame has been generated following
   // a page load. This stops |new_content_rendering_timeout_|, or prevents
   // the timer from running if the load commit message hasn't been received
   // yet.
   void OnFirstPaintAfterLoad();
 
@@ skipping 512 matching lines @@
   bool is_focused_;
 
   // Whether the view should send begin frame messages to its render widget.
   // This is state that may arrive before the view has been set and that must be
   // consistent with the state in the renderer, so this host handles it.
   bool needs_begin_frames_ = false;
 
   // This value indicates how long to wait before we consider a renderer hung.
   base::TimeDelta hung_renderer_delay_;
 
+  // This is the number of calls to SetHangMonitorKnownUnresponsive.
+  int known_unresponsive_renderer_count_ = 0;

[Charlie Reis, 2016/10/05 22:00:59]

When would this be more than one?

+
   // Stores the reason the hang_monitor_timeout_ has been started. Used to
   // report histograms if the renderer is hung.
   RenderWidgetHostDelegate::RendererUnresponsiveType hang_monitor_reason_;
 
   // This value indicates how long to wait for a new compositor frame from a
   // renderer process before clearing any previously displayed content.
   base::TimeDelta new_content_rendering_delay_;
 
 #if defined(OS_MACOSX)
   std::unique_ptr<device::PowerSaveBlocker> power_save_blocker_;
 #endif
 
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_