Removed CopyState() from NavigationManager, as it is unused.

ios/web/navigation/navigation_manager_impl.mm

 // Copyright 2013 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/navigation_manager_impl.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 341 matching lines @@
 
 std::unique_ptr<std::vector<BrowserURLRewriter::URLRewriter>>
 NavigationManagerImpl::GetTransientURLRewriters() {
   return std::move(transient_url_rewriters_);
 }
 
 void NavigationManagerImpl::RemoveTransientURLRewriters() {
   transient_url_rewriters_.reset();
 }
 
-void NavigationManagerImpl::CopyState(
-    NavigationManagerImpl* navigation_manager) {
-  SetSessionController([navigation_manager->GetSessionController() copy]);
-}
-
 int NavigationManagerImpl::GetIndexForOffset(int offset) const {
   int result = [session_controller_ pendingItemIndex] == -1
                    ? GetCurrentItemIndex()
                    : static_cast<int>([session_controller_ pendingItemIndex]);
 
   if (offset < 0) {
     if (GetTransientItem() && [session_controller_ pendingItemIndex] == -1) {
       // Going back from transient item that added to the end navigation stack
       // is a matter of discarding it as there is no need to move navigation
       // index back.
@@ skipping 73 matching lines @@
   const ScopedNavigationItemImplList& items = [session_controller_ items];
   while (index >= 0) {
     NavigationItem* item = items[index--].get();
     if (!client->IsAppSpecificURL(item->GetVirtualURL()))
       return item;
   }
   return nullptr;
 }
 
 }  // namespace web