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

chrome/browser/sessions/session_restore.cc

Index: chrome/browser/sessions/session_restore.cc
diff --git a/chrome/browser/sessions/session_restore.cc b/chrome/browser/sessions/session_restore.cc
index 49831a27f087a8f5ec11c6b7b8b9b58499f6cffd..eed1b4b4ee1e299ee3badeddea85d93a880f9d58 100644
--- a/chrome/browser/sessions/session_restore.cc
+++ b/chrome/browser/sessions/session_restore.cc
@@ -131,6 +131,8 @@ class SessionRestoreImpl : public content::NotificationObserver {
 
     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_; }