Add option to disallow the discarding of a tab that was previously discarded.

chrome/browser/memory/oom_priority_manager.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_MEMORY_OOM_PRIORITY_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_OOM_PRIORITY_MANAGER_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 35 matching lines @@
  public:
   OomPriorityManager();
   ~OomPriorityManager();
 
   // Number of discard events since Chrome started.
   int discard_count() const { return discard_count_; }
 
   // See member comment.
   bool recent_tab_discard() const { return recent_tab_discard_; }
 
-  void Start();
+  // If |discard_once| is set, tabs that get discarded once will never get
+  // discarded again.
+  void Start(bool discard_once);
   void Stop();
 
   // Returns the list of the stats for all renderers. Must be called on the UI
   // thread.
   TabStatsList GetTabStats();
 
   // Discards a tab to free the memory occupied by its renderer. The tab still
   // exists in the tab-strip; clicking on it will reload it. Returns true if it
   // successfully found a tab and discarded it.
   bool DiscardTab();
@@ skipping 39 matching lines @@
   // Adds all the stats of the tabs in |browser_list| into |stats_list|. If
   // |active_desktop| is true, we consider its first window as being active.
   void AddTabStats(BrowserList* browser_list,
                    bool active_desktop,
                    TabStatsList* stats_list);
 
   // Callback for when |update_timer_| fires. Takes care of executing the tasks
   // that need to be run periodically (see comment in implementation).
   void UpdateTimerCallback();
 
+  // Goes through a list of checks to see if a tab is allowed to be discarded by
+  // the automatic tab discarding mechanism. Note that this is not used when
+  // discarding a particular tab from about:discards.
+  bool CanDiscardTab(int64 target_web_contents_id) const;
+
   static bool CompareTabStats(TabStats first, TabStats second);
 
   // Called by the memory pressure listener when the memory pressure rises.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
   // Timer to periodically update the stats of the renderers.
   base::RepeatingTimer<OomPriorityManager> update_timer_;
 
   // Timer to periodically report whether a tab has been discarded since the
@@ skipping 14 matching lines @@
   // times for discontinuities caused by suspend/resume.
   base::TimeTicks last_adjust_time_;
 
   // Number of times we have discarded a tab, for statistics.
   int discard_count_;
 
   // Whether a tab discard event has occurred during the last time interval,
   // used for statistics normalized by usage.
   bool recent_tab_discard_;
 
+  // Whether we ever only discard a tab once.
+  bool discard_once_;
+
 #if defined(OS_CHROMEOS)
   scoped_ptr<OomPriorityManagerDelegate> delegate_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(OomPriorityManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_OOM_PRIORITY_MANAGER_H_