[Session restore] Expose lazy mode and fix browser tests.

chrome/browser/sessions/session_restore.cc

 // Copyright 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/sessions/session_restore.h"
 
 #include <algorithm>
 #include <list>
 #include <set>
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/alias.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/run_loop.h"
 #include "base/stl_util.h"
 #include "base/task/cancelable_task_tracker.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/search.h"
 #include "chrome/browser/sessions/session_restore_delegate.h"
 #include "chrome/browser/sessions/session_service.h"
@@ skipping 262 matching lines @@
         // No tab browsers were created and no URLs were supplied on the command
         // line. Open the new tab page.
         urls_to_open_.push_back(GURL(chrome::kChromeUINewTabURL));
       }
       AppendURLsToBrowser(browser, urls_to_open_);
       browser->window()->Show();
     }
 
     if (succeeded) {
       // Start Loading tabs.
-      SessionRestoreDelegate::RestoreTabs(contents_created, restore_started_);
+      bool active_only = SessionRestore::IsLoadingActiveTabsOnly();
+      SessionRestoreDelegate::RestoreTabs(contents_created, restore_started_,
+                                          active_only);
     }
 
     if (!synchronous_) {
       // If we're not synchronous we need to delete ourself.
       // NOTE: we must use DeleteLater here as most likely we're in a callback
       // from the history service which doesn't deal well with deleting the
       // object it is notifying.
       base::MessageLoop::current()->DeleteSoon(FROM_HERE, this);
 
       // The delete may take a while and at this point we no longer care about
@@ skipping 499 matching lines @@
 }
 
 // static
 SessionRestore::CallbackSubscription
     SessionRestore::RegisterOnSessionRestoredCallback(
         const base::Callback<void(int)>& callback) {
   return on_session_restored_callbacks()->Add(callback);
 }
 
 // static
+bool SessionRestore::IsLoadingActiveTabsOnly() {
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find("SessionRestoreBackgroundLoading");
+  if (!trial || trial->group_name() == "Restore")
+    return false;
+  return true;
+}
+
+// static
 base::CallbackList<void(int)>*
     SessionRestore::on_session_restored_callbacks_ = nullptr;