Creates BrowserTabStripTracker to consolidate common code

chrome/browser/memory/tab_manager.cc

 // 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.
 
 #include "chrome/browser/memory/tab_manager.h"
 
 #include <algorithm>
 #include <set>
 #include <vector>
 
@@ skipping 83 matching lines @@
 
   return -1;
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // TabManager
 
 TabManager::TabManager()
-    : discard_count_(0), recent_tab_discard_(false), discard_once_(false) {
+    : discard_count_(0),
+      recent_tab_discard_(false),
+      discard_once_(false),
+      browser_tab_strip_tracker_(this, nullptr, nullptr) {
 #if defined(OS_CHROMEOS)
   delegate_.reset(new TabManagerDelegate);
 #endif
-  BrowserList::AddObserver(this);
+  browser_tab_strip_tracker_.Init(
+      BrowserTabStripTracker::InitWith::ALL_BROWERS);
 }
 
 TabManager::~TabManager() {
   Stop();
-  for (chrome::BrowserIterator iterator; !iterator.done(); iterator.Next())
-    iterator->tab_strip_model()->RemoveObserver(this);
-
-  BrowserList::RemoveObserver(this);
 }
 
 void TabManager::Start(bool discard_once) {
   discard_once_ = discard_once;
   if (!update_timer_.IsRunning()) {
     update_timer_.Start(FROM_HERE,
                         TimeDelta::FromSeconds(kAdjustmentIntervalSeconds),
                         this, &TabManager::UpdateTimerCallback);
   }
   if (!recent_tab_discard_timer_.IsRunning()) {
@@ skipping 341 matching lines @@
 
   // For the moment we only do something when we reach a critical state.
   if (memory_pressure_level ==
       base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
     LogMemoryAndDiscardTab();
   }
   // TODO(skuhne): If more memory pressure levels are introduced, we might
   // consider to call PurgeBrowserMemory() before CRITICAL is reached.
 }
 
-void TabManager::OnBrowserAdded(Browser* browser) {
-  browser->tab_strip_model()->AddObserver(this);
-}
-
-void TabManager::OnBrowserRemoved(Browser* browser) {
-  browser->tab_strip_model()->RemoveObserver(this);
-}
-
 bool TabManager::IsAudioTab(WebContents* contents) const {
   if (contents->WasRecentlyAudible())
     return true;
   auto delta =
       TimeTicks::Now() - memory::TabDiscardState::LastAudioChangeTime(contents);
   return delta < TimeDelta::FromSeconds(kAudioProtectionTimeSeconds);
 }
 
 // static
 bool TabManager::CompareTabStats(TabStats first, TabStats second) {
@@ skipping 29 matching lines @@
   // sudden_termination_allowed false, and that covers too many common pages
   // with ad networks and statistics scripts.  Ideally we would like to check
   // for beforeUnload handlers, which are likely to present a dialog asking
   // if the user wants to discard state.  crbug.com/123049
 
   // Being more recently active is more important.
   return first.last_active > second.last_active;
 }
 
 }  // namespace memory