Remove unnecessary 'virtual' annotation from mojo

mojo/services/html_viewer/webstoragenamespace_impl.cc

 // 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.
 
 #include "mojo/services/html_viewer/webstoragenamespace_impl.h"
 
 #include <stdio.h>
 
 #include "third_party/WebKit/public/platform/WebStorageArea.h"
 
 namespace html_viewer {
 namespace {
 
 class DummyWebStorageAreaImpl : public blink::WebStorageArea {
  public:
-  virtual unsigned length() {
-    return 0;
-  }
-  virtual blink::WebString key(unsigned index) {
-    return blink::WebString();
-  }
-  virtual blink::WebString getItem(const blink::WebString& key) {
+  unsigned length() override { return 0; }
+  blink::WebString key(unsigned index) override { return blink::WebString(); }
+  blink::WebString getItem(const blink::WebString& key) override {
     return blink::WebString();
   }
 };
 
 }  // namespace
 
 WebStorageNamespaceImpl::WebStorageNamespaceImpl() {
 }
 
 WebStorageNamespaceImpl::~WebStorageNamespaceImpl() {
 }
 
 blink::WebStorageArea* WebStorageNamespaceImpl::createStorageArea(
     const blink::WebString& origin) {
   return new DummyWebStorageAreaImpl();
 }
 
 bool WebStorageNamespaceImpl::isSameNamespace(
     const blink::WebStorageNamespace&) const {
   return false;
 }
 
 }  // namespace html_viewer