Add experiment to disable loading of background tabs during session restore.

chrome/browser/sessions/session_restore_delegate.cc

 // 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.
 
 #include "chrome/browser/sessions/session_restore_delegate.h"
 
+#include "base/metrics/field_trial.h"
 #include "chrome/browser/sessions/session_restore_stats_collector.h"
 #include "chrome/browser/sessions/tab_loader.h"
 
 // static
 void SessionRestoreDelegate::RestoreTabs(
     const std::vector<RestoredTab>& tabs,
     const base::TimeTicks& restore_started) {
-  SessionRestoreStatsCollector::TrackTabs(tabs, restore_started);
-  TabLoader::RestoreTabs(tabs, restore_started);
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find("SessionRestoreBackgroundLoading");
+  // If there is no trial, enable experiment to get coverage on the perf
+  // waterfall.
+  bool active_only = true;
+  if (trial && trial->group_name() != "Disabled") {
+    TabLoader::RestoreTabs(tabs, restore_started);
+    active_only = false;
+  }
+  SessionRestoreStatsCollector::TrackTabs(tabs, restore_started, active_only);
 }