Creates BrowserTabStripTracker to consolidate common code

chrome/browser/memory/tab_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_TAB_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 
 #include <utility>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string16.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/memory/tab_stats.h"
-#include "chrome/browser/ui/browser_list_observer.h"
+#include "chrome/browser/ui/browser_tab_strip_tracker.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
 
 class BrowserList;
 class GURL;
 
 namespace memory {
 
 #if defined(OS_CHROMEOS)
 class TabManagerDelegate;
 #endif
 
 // The TabManager periodically updates (see
 // |kAdjustmentIntervalSeconds| in the source) the status of renderers
 // which are then used by the algorithm embedded here for priority in being
 // killed upon OOM conditions.
 //
 // The algorithm used favors killing tabs that are not selected, not pinned,
 // and have been idle for longest, in that order of priority.
 //
 // On Chrome OS (via the delegate), the kernel (via /proc/<pid>/oom_score_adj)
 // will be informed of each renderer's score, which is based on the status, so
 // in case Chrome is not able to relieve the pressure quickly enough and the
 // kernel is forced to kill processes, it will be able to do so using the same
 // algorithm as the one used here.
 //
 // Note that the browser tests are only active for platforms that use
 // TabManager (CrOS only for now) and need to be adjusted accordingly if
 // support for new platforms is added.
-class TabManager : public chrome::BrowserListObserver,
-                   public TabStripModelObserver {
+class TabManager : public TabStripModelObserver {
  public:
   TabManager();
   ~TabManager() override;
 
   // 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_; }
 
@@ skipping 61 matching lines @@
 
   // 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;
 
   // Called by the memory pressure listener when the memory pressure rises.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
-  // chrome::BrowserListObserver overrides.
-  void OnBrowserAdded(Browser* browser) override;
-  void OnBrowserRemoved(Browser* browser) override;
-
   // TabStripModelObserver overrides.
   void TabChangedAt(content::WebContents* contents,
                     int index,
                     TabChangeType change_type) override;
 
   // Returns true if the tab is currently playing audio or has played audio
   // recently.
   bool IsAudioTab(content::WebContents* contents) const;
 
   // Returns true if |first| is considered less desirable to be killed than
@@ skipping 28 matching lines @@
   // 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<TabManagerDelegate> delegate_;
 #endif
 
+  BrowserTabStripTracker browser_tab_strip_tracker_;
+
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_H_