Created a DownloadManager interface, for use in unit tests..

content/browser/download/download_file.h

 // Copyright (c) 2011 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_FILE_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_FILE_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "content/browser/download/base_file.h"
 #include "content/browser/download/download_id.h"
 #include "content/browser/download/download_request_handle.h"
 #include "content/browser/download/download_types.h"
 #include "content/common/content_export.h"
 
 struct DownloadCreateInfo;
-class DownloadManager;
+class DownloadManagerInterface;
 class ResourceDispatcherHost;
 
 // These objects live exclusively on the download thread and handle the writing
 // operations for one download. These objects live only for the duration that
 // the download is 'in progress': once the download has been completed or
 // cancelled, the DownloadFile is destroyed.
 class CONTENT_EXPORT DownloadFile : public BaseFile {
  public:
   DownloadFile(const DownloadCreateInfo* info,
                const DownloadRequestHandle& request_handle,
-               DownloadManager* download_manager);
+               DownloadManagerInterface* download_manager);
   virtual ~DownloadFile();
 
   // Cancels the download request associated with this file.
   void CancelDownloadRequest();
 
   int id() const { return id_.local(); }
-  DownloadManager* GetDownloadManager();
+  DownloadManagerInterface* GetDownloadManager();
   const DownloadId& global_id() const { return id_; }
 
   virtual std::string DebugString() const;
 
   // Appends the passed the number between parenthesis the path before the
   // extension.
   static void AppendNumberToPath(FilePath* path, int number);
 
   // Attempts to find a number that can be appended to that path to make it
   // unique. If |path| does not exist, 0 is returned.  If it fails to find such
@@ skipping 14 matching lines @@
  private:
   // The unique identifier for this download, assigned at creation by
   // the DownloadFileManager for its internal record keeping.
   DownloadId id_;
 
   // The handle to the request information.  Used for operations outside the
   // download system, specifically canceling a download.
   DownloadRequestHandle request_handle_;
 
   // DownloadManager this download belongs to.
-  scoped_refptr<DownloadManager> download_manager_;
+  scoped_refptr<DownloadManagerInterface> download_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadFile);
 };
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_FILE_H_