Use TabLoader in TabRestoreService.

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 <stddef.h>
 
 #include <list>
@@ skipping 43 matching lines @@
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // TabLoaderCallback:
   void SetTabLoadingEnabled(bool enable_tab_loading) override;
 
   // Called to start restoring tabs.
   static void RestoreTabs(const std::vector<RestoredTab>& tabs,
                           const base::TimeTicks& restore_started);
 
+  // Limit the number of loaded tabs.
+  // Value of 0 restores default behavior. In test mode command line flags and
+  // free memory size are not taken into account.
+  static void SetMaxLoadedTabCountForTest(size_t value);

[sky, 2017/03/02 19:12:05]

I prefer keeping the public api clean. Instead of this, make the test a friend.
If you need multiple tests to access it, friend a TabLoaderTestApi class that is
only built in tests.

[Michael K. (Yandex Team), 2017/03/03 08:26:37]

Done.

+
  private:
   FRIEND_TEST_ALL_PREFIXES(TabLoaderTest, OnMemoryStateChange);
 
   friend class base::RefCounted<TabLoader>;
 
   using TabsLoading = std::set<content::NavigationController*>;
   using TabsToLoad = std::list<content::NavigationController*>;
 
   explicit TabLoader(base::TimeTicks restore_started);
   ~TabLoader() override;
@@ skipping 63 matching lines @@
   // True if the tab loading is enabled.
   bool loading_enabled_;
 
   // The set of tabs we've initiated loading on. This does NOT include the
   // selected tabs.
   TabsLoading tabs_loading_;
 
   // The tabs we need to load.
   TabsToLoad tabs_to_load_;
 
+  // The number of tabs started to load.

[sky, 2017/03/02 19:12:05]

Document this value never decreases.

[Michael K. (Yandex Team), 2017/03/03 08:26:37]

Done.

+  size_t started_to_load_count_;
+
   base::OneShotTimer 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_