[iOS] Refactoring web CRWSessionController user agent code.

ios/web/public/test/fakes/test_navigation_manager.mm

 // Copyright 2016 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 "ios/web/public/test/fakes/test_navigation_manager.h"
 
 namespace web {
 
 TestNavigationManager::TestNavigationManager()
     : pending_item_(nullptr),
@@ skipping 36 matching lines @@
   pending_item_ = item;
 }
 
 web::NavigationItem* TestNavigationManager::GetTransientItem() const {
   NOTREACHED();
   return nullptr;
 }
 
 void TestNavigationManager::DiscardNonCommittedItems() {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::LoadIfNecessary() {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::LoadURLWithParams(
     const NavigationManager::WebLoadParams& params) {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::AddTransientURLRewriter(
     BrowserURLRewriter::URLRewriter rewriter) {
   NOTREACHED();
-  return;
 }
 
 int TestNavigationManager::GetItemCount() const {
   NOTREACHED();
   return 0;
 }
 
 web::NavigationItem* TestNavigationManager::GetItemAtIndex(size_t index) const {
   NOTREACHED();
   return nullptr;
@@ skipping 29 matching lines @@
   return false;
 }
 
 bool TestNavigationManager::CanGoToOffset(int offset) const {
   NOTREACHED();
   return false;
 }
 
 void TestNavigationManager::GoBack() {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::GoForward() {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::GoToIndex(int index) {
   NOTREACHED();
-  return;
 }
 
 void TestNavigationManager::Reload(bool check_for_repost) {
   NOTREACHED();
-  return;
+}
+
+void TestNavigationManager::OverrideDesktopUserAgentForNextPendingItem() {
+  NOTREACHED();
 }
 
 }  // namespace web