content: Cleanup class/struct forward declarations

content/browser/download/download_request_core.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_REQUEST_CORE_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_REQUEST_CORE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 12 matching lines @@
 class PowerSaveBlocker;
 }  // namespace device
 
 namespace net {
 class HttpResponseHeaders;
 class URLRequest;
 class URLRequestStatus;
 }  // namespace net
 
 namespace content {
-class DownloadManagerImpl;
 class ByteStreamReader;
 class ByteStreamWriter;
 struct DownloadCreateInfo;
 
 // This class encapsulates the core logic for reading data from a URLRequest and
 // writing it into a ByteStream. It's common to both DownloadResourceHandler and
 // UrlDownloader.
 //
 // Created, lives on and dies on the IO thread.
 class CONTENT_EXPORT DownloadRequestCore
@@ skipping 123 matching lines @@
 
   // Each successful OnWillRead will yield a buffer of this size.
   static const int kReadBufSize = 32768;   // bytes
 
   DISALLOW_COPY_AND_ASSIGN(DownloadRequestCore);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_REQUEST_CORE_H_