Remove base/win/metro.{cc|h} and some associated code

chrome/browser/tab_contents/navigation_metrics_recorder.h

 // Copyright (c) 2012 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_TAB_CONTENTS_NAVIGATION_METRICS_RECORDER_H_
 #define CHROME_BROWSER_TAB_CONTENTS_NAVIGATION_METRICS_RECORDER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 class NavigationMetricsRecorder
     : public content::WebContentsObserver,
       public content::WebContentsUserData<NavigationMetricsRecorder> {
  public:
   ~NavigationMetricsRecorder() override;
 
  private:
   explicit NavigationMetricsRecorder(content::WebContents* web_contents);
   friend class content::WebContentsUserData<NavigationMetricsRecorder>;
 
   // content::WebContentsObserver overrides:
   void DidNavigateMainFrame(
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) override;
 
-  void DidStartLoading() override;
-
   DISALLOW_COPY_AND_ASSIGN(NavigationMetricsRecorder);
 };
 
 #endif  // CHROME_BROWSER_TAB_CONTENTS_NAVIGATION_METRICS_RECORDER_H_