[Tab Metrics] Measure FP, FCP and FMP for Foreground Tab during Session Restore

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 <stddef.h>
 
 #include <algorithm>
 #include <list>
@@ skipping 113 matching lines @@
          it != active_session_restorers->end(); ++it) {
       if ((*it)->profile_ == profile)
         break;
     }
     DCHECK(it == active_session_restorers->end());
 
     active_session_restorers->insert(this);
 
     keep_alive_.reset(new ScopedKeepAlive(KeepAliveOrigin::SESSION_RESTORE,
                                           KeepAliveRestartOption::DISABLED));
+    for (auto& observer : SessionRestore::observers())
+      observer.OnSessionRestoreStartedLoadingTabs();

[ducbui, 2017/07/04 05:34:39]

I move the start of session restore to here. Thereby, we will have multiple
start signals but still only one session restore stop signal, so we still can
cover the start of the first session restore to the last session restore.

[ducbui, 2017/07/04 15:28:25]

The revision of the session restore start signal does not work because it causes
multi stop signals as well (I thought there would be only one stop signal). Some
tests failed because of this:
https://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium...

   }
 
   bool synchronous() const { return synchronous_; }
 
   Browser* Restore() {
     SessionService* session_service =
         SessionServiceFactory::GetForProfile(profile_);
     DCHECK(session_service);
     session_service->GetLastSession(
         base::Bind(&SessionRestoreImpl::OnGotSession, base::Unretained(this)),
@@ skipping 730 matching lines @@
   observers().RemoveObserver(observer);
 }
 
 // static
 base::CallbackList<void(int)>*
     SessionRestore::on_session_restored_callbacks_ = nullptr;
 
 // static
 base::ObserverList<SessionRestoreObserver>* SessionRestore::observers_ =
     nullptr;