[TabMetrics] Add signals that mark the start and end of session restore.

chrome/browser/sessions/tab_loader.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/tab_loader.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/memory/memory_coordinator_client_registry.h"
@@ skipping 85 matching lines @@
       loading_enabled_(true),
       started_to_load_count_(0),
       restore_started_(restore_started) {
   stats_collector_ = new SessionRestoreStatsCollector(
       restore_started,
       base::MakeUnique<
           SessionRestoreStatsCollector::UmaStatsReportingDelegate>());
   shared_tab_loader_ = this;
   this_retainer_ = this;
   base::MemoryCoordinatorClientRegistry::GetInstance()->Register(this);
+  for (auto& observer : SessionRestore::observers())
+    observer.OnSessionRestoreStartedLoadingTabs();
 }
 
 TabLoader::~TabLoader() {
   DCHECK(tabs_loading_.empty() && tabs_to_load_.empty());
   DCHECK(shared_tab_loader_ == this);
   shared_tab_loader_ = nullptr;
   base::MemoryCoordinatorClientRegistry::GetInstance()->Unregister(this);
+  for (auto& observer : SessionRestore::observers())
+    observer.OnSessionRestoreFinishedLoadingTabs();
 }
 
 void TabLoader::StartLoading(const std::vector<RestoredTab>& tabs) {
   // Add the tabs to the list of tabs loading/to load and register them for
   // notifications. Also, restore the favicons of the background tabs (the title
   // has already been set by now).This avoids having blank icons in case the
   // restore is halted due to memory pressure. Also, when multiple tabs are
   // restored to a single window, the title may not appear, and the user will
   // have no way of finding out which tabs corresponds to which page if the icon
   // is a generic grey one.
@@ skipping 185 matching lines @@
     // memory pressure.
     stats_collector_->DeferTab(tab);
   }
   // By calling |LoadNextTab| explicitly, we make sure that the
   // |NOTIFICATION_SESSION_RESTORE_DONE| event gets sent.
   LoadNextTab();
 }
 
 // static
 TabLoader* TabLoader::shared_tab_loader_ = nullptr;