Use TabLoader in TabRestoreService.

chrome/browser/sessions/tab_loader.h

Index: chrome/browser/sessions/tab_loader.h
diff --git a/chrome/browser/sessions/tab_loader.h b/chrome/browser/sessions/tab_loader.h
index 81c6dd0b1e18fc89ea341b176cf3fc1deac35578..a8dffd92da48fdd487cd5425a0ead3d34cd973b6 100644
--- a/chrome/browser/sessions/tab_loader.h
+++ b/chrome/browser/sessions/tab_loader.h
@@ -61,6 +61,11 @@ class TabLoader : public content::NotificationObserver,
   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);
 
@@ -144,6 +149,9 @@ class TabLoader : public content::NotificationObserver,
   // 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.