Update {virtual,override} to follow C++11 style in content.

content/browser/web_contents/web_contents_view_overscroll_animator_slider_mac.mm

 // Copyright 2014 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.
 
 #import <QuartzCore/QuartzCore.h>
 
 #include "content/browser/web_contents/web_contents_view_overscroll_animator_slider_mac.h"
 
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/web_contents_observer.h"
@@ skipping 54 matching lines @@
 
 // Helper Class (WebContentsPaintObserver) -------------------------------------
 
 namespace overscroll_animator {
 class WebContentsPaintObserver : public content::WebContentsObserver {
  public:
   WebContentsPaintObserver(content::WebContents* web_contents,
                            OverscrollAnimatorSliderView* slider_view)
       : WebContentsObserver(web_contents), slider_view_(slider_view) {}
 
-  virtual void DidFirstVisuallyNonEmptyPaint() override {
+  void DidFirstVisuallyNonEmptyPaint() override {
     [slider_view_ webContentsFinishedNonEmptyPaint];
   }
 
  private:
   OverscrollAnimatorSliderView* slider_view_;  // Weak reference.
 };
 }  // namespace overscroll_animator
 
 // OverscrollAnimatorSliderView Implementation ---------------------------------
 
@@ skipping 164 matching lines @@
       [self reset];
   }];
 
   // Animate the moving view to its initial position.
   [[view animator] setFrameOrigin:[self frameOriginWithProgress:kMinProgress]];
 
   [NSAnimationContext endGrouping];
 }
 
 @end