[Sessions] Add detailed logging of SessionRestore events.

chrome/browser/sessions/tab_loader.h

 // Copyright 2015 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_SESSIONS_TAB_LOADER_H_
 #define CHROME_BROWSER_SESSIONS_TAB_LOADER_H_
 
 #include <list>
 #include <set>
 
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/timer/timer.h"
 #include "chrome/browser/sessions/session_restore_delegate.h"
 #include "chrome/browser/sessions/tab_loader_delegate.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 namespace content {
 class NavigationController;
 class RenderWidgetHost;
 }
 
+class SessionRestoreStatsCollector;
+
 // TabLoader is responsible for loading tabs after session restore has finished
 // creating all the tabs. Tabs are loaded after a previously tab finishes
 // loading or a timeout is reached. If the timeout is reached before a tab
 // finishes loading the timeout delay is doubled.
 //
 // TabLoader keeps a reference to itself when it's loading. When it has finished
 // loading, it drops the reference. If another profile is restored while the
 // TabLoader is loading, it will schedule its tabs to get loaded by the same
 // TabLoader. When doing the scheduling, it holds a reference to the TabLoader.
 //
@@ skipping 91 matching lines @@
 
   base::OneShotTimer<TabLoader> force_load_timer_;
 
   // The time the restore process started.
   base::TimeTicks restore_started_;
 
   // For keeping TabLoader alive while it's loading even if no
   // SessionRestoreImpls reference it.
   scoped_refptr<TabLoader> this_retainer_;
 
+  // The SessionRestoreStatsCollector associated with this TabLoader. This is
+  // explicitly referenced so that it can be notified of deferred tab loads due
+  // to memory pressure.
+  scoped_refptr<SessionRestoreStatsCollector> stats_collector_;
+
   static TabLoader* shared_tab_loader_;
 
   DISALLOW_COPY_AND_ASSIGN(TabLoader);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_TAB_LOADER_H_