Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

net/ftp/ftp_network_layer.h

 // Copyright (c) 2010 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.
 
 #ifndef NET_FTP_FTP_NETWORK_LAYER_H_
 #define NET_FTP_FTP_NETWORK_LAYER_H_
 #pragma once
 
 #include "base/ref_counted.h"
 #include "net/ftp/ftp_transaction_factory.h"
 
 namespace net {
 
 class FtpNetworkSession;
-class FtpAuthCache;
 class HostResolver;
 
 class FtpNetworkLayer : public FtpTransactionFactory {
  public:
   explicit FtpNetworkLayer(HostResolver* host_resolver);
   ~FtpNetworkLayer();
 
   static FtpTransactionFactory* CreateFactory(HostResolver* host_resolver);
 
   // FtpTransactionFactory methods:
   virtual FtpTransaction* CreateTransaction();
   virtual void Suspend(bool suspend);
 
  private:
   scoped_refptr<FtpNetworkSession> session_;
   bool suspended_;
 };
 
 }  // namespace net
 
 #endif  // NET_FTP_FTP_NETWORK_LAYER_H_