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

chrome/browser/sessions/session_restore_stats_collector.cc

Index: chrome/browser/sessions/session_restore_stats_collector.cc
diff --git a/chrome/browser/sessions/session_restore_stats_collector.cc b/chrome/browser/sessions/session_restore_stats_collector.cc
index b24d561c8280d65623a1a9e060884edccb256c7a..2c0e648845e914d796add9825244e7d734731f3d 100644
--- a/chrome/browser/sessions/session_restore_stats_collector.cc
+++ b/chrome/browser/sessions/session_restore_stats_collector.cc
@@ -20,20 +20,24 @@ using content::WebContents;
 // static
 void SessionRestoreStatsCollector::TrackTabs(
     const std::vector<SessionRestoreDelegate::RestoredTab>& tabs,
-    const base::TimeTicks& restore_started) {
+    const base::TimeTicks& restore_started,
+    bool active_only) {
   if (!shared_collector_)
-    shared_collector_ = new SessionRestoreStatsCollector(restore_started);
+    shared_collector_ =
+        new SessionRestoreStatsCollector(restore_started, active_only);
 
   shared_collector_->AddTabs(tabs);
 }
 
 SessionRestoreStatsCollector::SessionRestoreStatsCollector(
-    const base::TimeTicks& restore_started)
+    const base::TimeTicks& restore_started,
+    bool active_only)
     : got_first_foreground_load_(false),
       got_first_paint_(false),
       restore_started_(restore_started),
       tab_count_(0),
-      max_parallel_tab_loads_(0) {
+      max_parallel_tab_loads_(0),
+      active_only_(active_only) {
   this_retainer_ = this;
   registrar_.Add(
       this, content::NOTIFICATION_RENDER_WIDGET_HOST_DID_UPDATE_BACKING_STORE,
@@ -163,7 +167,12 @@ void SessionRestoreStatsCollector::Observe(
 
 void SessionRestoreStatsCollector::AddTabs(
     const std::vector<SessionRestoreDelegate::RestoredTab>& tabs) {
+  tab_count_ += tabs.size();
   for (auto& tab : tabs) {
+    // If we are only restoring active tabs and the tab is not active, nothing
+    // to do.
+    if (active_only_ && !tab.is_active)

[sky, 2015/04/03 22:04:46]

Actually, one nit. Pass active_only to this function and nuke the field.

+      continue;
     RegisterForNotifications(&tab.contents->GetController());
     if (tab.is_active) {
       RenderWidgetHost* render_widget_host =
@@ -218,7 +227,6 @@ void SessionRestoreStatsCollector::RegisterForNotifications(
                  content::Source<NavigationController>(tab));
   registrar_.Add(this, content::NOTIFICATION_LOAD_START,
                  content::Source<NavigationController>(tab));
-  ++tab_count_;
   tabs_tracked_.insert(tab);
 }