Added UkmPageLoadMetricsObserver which sends top-level metrics to UKM

components/ukm/ukm_source.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 COMPONENTS_UKM_UKM_SOURCE_H_
 #define COMPONENTS_UKM_UKM_SOURCE_H_
 
 #include <stddef.h>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "url/gurl.h"
 
 namespace ukm {
 
 class Source;
 
 // Contains UKM data for a single navigation entry.
 class UkmSource {
  public:
   UkmSource();
   ~UkmSource();
 
   const GURL& committed_url() const { return committed_url_; }
   void set_committed_url(const GURL& committed_url) {
     committed_url_ = committed_url;
   }
 
-  base::Time navigation_start() const { return navigation_start_; }
-  void set_navigation_start(base::Time navigation_start) {
-    navigation_start_ = navigation_start;
-  }
-
   base::TimeDelta first_contentful_paint() const {
     return first_contentful_paint_;
   }
   void set_first_contentful_paint(base::TimeDelta first_contentful_paint) {
     first_contentful_paint_ = first_contentful_paint;
   }
 
   // Serializes the members of the class into the supplied proto.
   void PopulateProto(Source* proto_source);
 
  private:
   GURL committed_url_;
-  base::Time navigation_start_;
   base::TimeDelta first_contentful_paint_;
 
   DISALLOW_COPY_AND_ASSIGN(UkmSource);
 };
 
 }  // namespace ukm
 
 #endif  // COMPONENTS_UKM_UKM_SOURCE_H_