[Navigation Experiment] Add WKBasedNavigationManagerImpl.

ios/web/navigation/session_storage_builder.mm

 // Copyright 2015 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/navigation/session_storage_builder.h"
 
 #include <memory>
 
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
@@ skipping 72 matching lines @@
     items[index] = std::move(item_impl);
   }
   NSUInteger last_committed_item_index = storage.lastCommittedItemIndex;
   base::scoped_nsobject<CRWSessionController> session_controller(
       [[CRWSessionController alloc]
             initWithBrowserState:nullptr
                  navigationItems:std::move(items)
           lastCommittedItemIndex:last_committed_item_index]);
   [session_controller setPreviousItemIndex:storage.previousItemIndex];
 
-  auto navigation_manager = base::MakeUnique<LegacyNavigationManagerImpl>();
-  navigation_manager->SetSessionController(session_controller);
-  web_state->navigation_manager_.reset(navigation_manager.release());
+  web_state->navigation_manager_->SetSessionController(session_controller);
 
   SessionCertificatePolicyCacheStorageBuilder cert_builder;
   std::unique_ptr<SessionCertificatePolicyCacheImpl> cert_policy_cache =
       cert_builder.BuildSessionCertificatePolicyCache(
           storage.certPolicyCacheStorage);
   if (!cert_policy_cache)
     cert_policy_cache = base::MakeUnique<SessionCertificatePolicyCacheImpl>();
   web_state->certificate_policy_cache_ = std::move(cert_policy_cache);
   web::SerializableUserDataManager::FromWebState(web_state)
       ->AddSerializableUserData(storage.userData);
 }
 
 }  // namespace web