Added const getter for WebState's NavigationManager.

ios/web/public/test/test_web_state.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 "ios/web/public/test/test_web_state.h"
 
 #include <stdint.h>
 
 #include "base/callback.h"
 
@@ skipping 21 matching lines @@
 }
 
 void TestWebState::SetWebUsageEnabled(bool enabled) {
   web_usage_enabled_ = enabled;
 }
 
 UIView* TestWebState::GetView() {
   return nullptr;
 }
 
+const NavigationManager* TestWebState::GetNavigationManager() const {
+  return nullptr;
+}
+
 NavigationManager* TestWebState::GetNavigationManager() {
   return nullptr;
 }
 
 CRWJSInjectionReceiver* TestWebState::GetJSInjectionReceiver() const {
   return nullptr;
 }
 
 void TestWebState::ExecuteJavaScript(const base::string16& javascript) {}
 
@@ skipping 82 matching lines @@
 shell::InterfaceRegistry* TestWebState::GetMojoInterfaceRegistry() {
   return nullptr;
 }
 
 base::WeakPtr<WebState> TestWebState::AsWeakPtr() {
   NOTREACHED();
   return base::WeakPtr<WebState>();
 }
 
 }  // namespace web