Make BootTimesLoader marker usage thread safe

chrome/browser/chromeos/boot_times_loader.h

Index: chrome/browser/chromeos/boot_times_loader.h
diff --git a/chrome/browser/chromeos/boot_times_loader.h b/chrome/browser/chromeos/boot_times_loader.h
index 0cae34f1d35762f1ede1ebfdad8229e37f208493..accc8b527721d3fde3f577cb755e0faf1c22c67f 100644
--- a/chrome/browser/chromeos/boot_times_loader.h
+++ b/chrome/browser/chromeos/boot_times_loader.h
@@ -140,6 +140,11 @@ class BootTimesLoader
     base::Time time() const { return time_; }
     bool send_to_uma() const { return send_to_uma_; }
 
+    // comparitor for sorting
+    bool operator<(const TimeMarker& other) const {
+      return time_ < other.time_;
+    }
+
    private:
     friend class std::vector<TimeMarker>;
     std::string name_;
@@ -159,7 +164,9 @@ class BootTimesLoader
   static void WriteTimes(const std::string base_name,
                          const std::string uma_name,
                          const std::string uma_prefix,
-                         const std::vector<TimeMarker> login_times);
+                         std::vector<TimeMarker> login_times);
+  static void AddMarker(std::vector<TimeMarker>* vector, TimeMarker marker);
+
   void LoginDone();
 
   // Used to hold the stats at main().