Enable strict-virtual-specifiers for iOS builds.

ios/web/navigation/navigation_item_impl_unittest.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.
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
 #include "ios/web/navigation/navigation_item_impl.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/gtest_mac.h"
 #include "testing/platform_test.h"
 
 namespace web {
 namespace {
 
 class NavigationItemTest : public PlatformTest {
  protected:
-  virtual void SetUp() {
-    item_.reset(new NavigationItemImpl());
-  }
+  void SetUp() override { item_.reset(new NavigationItemImpl()); }
 
   scoped_ptr<NavigationItemImpl> item_;
 };
 
 // TODO(rohitrao): Add and adapt tests from NavigationEntryImpl.
 TEST_F(NavigationItemTest, Dummy) {
   const GURL url("http://init.test");
   item_->SetURL(url);
   EXPECT_TRUE(item_->GetURL().is_valid());
 }
 
 }  // namespace
 }  // namespace web