Adding previews information to PLM UKM

chrome/browser/page_load_metrics/page_load_tracker.h

 // Copyright 2016 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_PAGE_LOAD_TRACKER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_TRACKER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 252 matching lines @@
   void MediaStartedPlaying(
       const content::WebContentsObserver::MediaPlayerInfo& video_type,
       bool is_in_main_frame);
 
   // Invoked on navigations where a navigation delay was added by the
   // DelayNavigationThrottle. This is a temporary method that will be removed
   // once the experiment is complete.
   void OnNavigationDelayComplete(base::TimeDelta scheduled_delay,
                                  base::TimeDelta actual_delay);
 
+  ukm::SourceId source_id() const { return source_id_; }
+
  private:
   // This function converts a TimeTicks value taken in the browser process
   // to navigation_start_ if:
   // - base::TimeTicks is not comparable across processes because the clock
   // is not system wide monotonic.
   // - *event_time < navigation_start_
   void ClampBrowserTimestampIfInterProcessTimeTickSkew(
       base::TimeTicks* event_time);
 
   void UpdatePageEndInternal(PageEndReason page_end_reason,
@@ skipping 86 matching lines @@
   PageLoadMetricsUpdateDispatcher metrics_update_dispatcher_;
 
   const ukm::SourceId source_id_;
 
   DISALLOW_COPY_AND_ASSIGN(PageLoadTracker);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_PAGE_LOAD_TRACKER_H_