Reland fast tab closure behind a flag

chrome/browser/ui/tab_contents/core_tab_helper.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 CHROME_BROWSER_UI_TAB_CONTENTS_CORE_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_TAB_CONTENTS_CORE_TAB_HELPER_H_
 
 #include "base/time/time.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
@@ skipping 13 matching lines @@
   string16 GetStatusText() const;
 
   // Notification that tab closing has started.  This can be called multiple
   // times, subsequent calls are ignored.
   void OnCloseStarted();
 
   // Notification that tab closing was cancelled. This can happen when a user
   // cancels a window close via another tab's beforeunload dialog.
   void OnCloseCanceled();
 
+  // Set the time during close when unload is started. Normally, this is set
+  // after the beforeunload dialog. However, for a window close, it is set
+  // after all the beforeunload dialogs have finished.
+  void OnUnloadStarted();
+
+  // Set the time during close when the tab is no longer visible.
+  void OnUnloadDetachedStarted();
+
   CoreTabHelperDelegate* delegate() const { return delegate_; }
   void set_delegate(CoreTabHelperDelegate* d) { delegate_ = d; }
 
   void set_new_tab_start_time(const base::TimeTicks& time) {
     new_tab_start_time_ = time;
   }
 
   base::TimeTicks new_tab_start_time() const { return new_tab_start_time_; }
 
  private:
@@ skipping 13 matching lines @@
   // The time when we started to create the new tab page.  This time is from
   // before we created this WebContents.
   base::TimeTicks new_tab_start_time_;
 
   // The time that we started to close this WebContents.
   base::TimeTicks close_start_time_;
 
   // The time when onbeforeunload ended.
   base::TimeTicks before_unload_end_time_;
 
+  // The time when the tab was removed from view during close.
+  base::TimeTicks unload_detached_start_time_;
+
   DISALLOW_COPY_AND_ASSIGN(CoreTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_TAB_CONTENTS_CORE_TAB_HELPER_H_