Add metrics for DelayNavigationThrottle

chrome/browser/page_load_metrics/experiments/delay_navigation_throttle.h

 // Copyright 2017 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.
 
 #ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_
 
 #include <memory>
 
 #include "base/feature_list.h"
@@ skipping 42 matching lines @@
 
   // content::NavigationThrottle:
   content::NavigationThrottle::ThrottleCheckResult WillStartRequest() override;
 
  private:
   void OnDelayComplete();
 
   const scoped_refptr<base::TaskRunner> task_runner_;
   const base::TimeDelta navigation_delay_;
 
+  // The time we added a delay to this navigation.
+  base::TimeTicks delay_start_time_;
+
   // This has to be the last member of the class.
   base::WeakPtrFactory<DelayNavigationThrottle> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DelayNavigationThrottle);
 };
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_EXPERIMENTS_DELAY_NAVIGATION_THROTTLE_H_