Plumb experiment flags through page_load_metrics and add a new observer

components/page_load_metrics/browser/page_load_metrics_observer.cc

 // Copyright 2015 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 "components/page_load_metrics/browser/page_load_metrics_observer.h"
 
 namespace page_load_metrics {
 
-PageLoadExtraInfo::PageLoadExtraInfo(
-    base::TimeDelta first_background_time,
-    base::TimeDelta first_foreground_time,
-    bool started_in_foreground,
-    const GURL& committed_url,
-    base::TimeDelta time_to_commit,
-    UserAbortType abort_type,
-    base::TimeDelta time_to_abort)
+PageLoadExtraInfo::PageLoadExtraInfo(base::TimeDelta first_background_time,
+                                     base::TimeDelta first_foreground_time,
+                                     bool started_in_foreground,
+                                     const GURL& committed_url,
+                                     base::TimeDelta time_to_commit,
+                                     UserAbortType abort_type,
+                                     base::TimeDelta time_to_abort,
+                                     const PageLoadMetadata& metadata)
     : first_background_time(first_background_time),
       first_foreground_time(first_foreground_time),
       started_in_foreground(started_in_foreground),
       committed_url(committed_url),
       time_to_commit(time_to_commit),
       abort_type(abort_type),
-      time_to_abort(time_to_abort) {}
+      time_to_abort(time_to_abort),
+      metadata(metadata) {}
 
 }  // namespace page_load_metrics