Unbreak tabs.onRemove extension API in face of fast tab closure

chrome/browser/ui/tab_contents/core_tab_helper.h

Index: chrome/browser/ui/tab_contents/core_tab_helper.h
diff --git a/chrome/browser/ui/tab_contents/core_tab_helper.h b/chrome/browser/ui/tab_contents/core_tab_helper.h
index e5a37dda8e194f58fdda85e7c7ae438791c5c1a9..0fde2e45a3e11a9a24fb42506f26c0647493f127 100644
--- a/chrome/browser/ui/tab_contents/core_tab_helper.h
+++ b/chrome/browser/ui/tab_contents/core_tab_helper.h
@@ -23,6 +23,10 @@ class CoreTabHelper : public content::WebContentsObserver,
   // Returns a human-readable description the tab's loading state.
   string16 GetStatusText() const;
 
+  // True if view is in the process of being detached from it's containing tab
+  // as part of tab closure.
+  bool GetWebContentsDetachedToClose() const;
+
   // Notification that tab closing has started.  This can be called multiple
   // times, subsequent calls are ignored.
   void OnCloseStarted();
@@ -36,6 +40,9 @@ class CoreTabHelper : public content::WebContentsObserver,
   // after all the beforeunload dialogs have finished.
   void OnUnloadStarted();
 
+  // Called just before making the tab invisible on close.
+  void OnUnloadAboutToDetach();
+
   // Set the time during close when the tab is no longer visible.
   void OnUnloadDetachedStarted();
 
@@ -75,6 +82,9 @@ class CoreTabHelper : public content::WebContentsObserver,
   // The time when the tab was removed from view during close.
   base::TimeTicks unload_detached_start_time_;
 
+  // True if the tab was removed from a view during close.
+  bool detached_as_part_of_unload_;
+
   DISALLOW_COPY_AND_ASSIGN(CoreTabHelper);
 };