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

chrome/browser/sessions/session_restore_delegate.cc

Index: chrome/browser/sessions/session_restore_delegate.cc
diff --git a/chrome/browser/sessions/session_restore_delegate.cc b/chrome/browser/sessions/session_restore_delegate.cc
index a24167ae1f24bfbbbee5a6f895ec54570c6097ca..e1b8d823040f72235ac821546ff4aaba548c07e6 100644
--- a/chrome/browser/sessions/session_restore_delegate.cc
+++ b/chrome/browser/sessions/session_restore_delegate.cc
@@ -4,6 +4,7 @@
 
 #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"
 
@@ -11,6 +12,14 @@
 void SessionRestoreDelegate::RestoreTabs(
     const std::vector<RestoredTab>& tabs,
     const base::TimeTicks& restore_started) {
-  SessionRestoreStatsCollector::TrackTabs(tabs, restore_started);
-  TabLoader::RestoreTabs(tabs, restore_started);
+  // TODO(georgesak): make tests aware of that behavior so that they succeed if
+  // tab loading is disabled.
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find("SessionRestoreBackgroundLoading");
+  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);
 }