Created an interface for DownloadFile, for use in unit tests.

content/browser/download/save_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_SAVE_FILE_H_
 #define CONTENT_BROWSER_DOWNLOAD_SAVE_FILE_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/browser/download/base_file.h"
 #include "content/browser/download/save_types.h"
 
 // SaveFile ----------------------------------------------------------------
 
 // These objects live exclusively on the file thread and handle the writing
 // operations for one save item. These objects live only for the duration that
 // the saving job is 'in progress': once the saving job has been completed or
 // canceled, the SaveFile is destroyed. One SaveFile object represents one item
 // in a save session.
-class SaveFile : public BaseFile {
+class SaveFile {
  public:
   explicit SaveFile(const SaveFileCreateInfo* info);
   virtual ~SaveFile();
 
+  // BaseFile delegated functions.
+  net::Error Initialize(bool calculate_hash);
+  net::Error AppendDataToFile(const char* data, size_t data_len);
+  net::Error Rename(const FilePath& full_path);
+  void Detach();
+  void Cancel();
+  void Finish();
+  void AnnotateWithSourceInformation();
+  FilePath FullPath() const;
+  bool InProgress() const;
+  int64 BytesSoFar() const;
+  bool GetSha256Hash(std::string* hash);
+  std::string DebugString() const;
+
   // Accessors.
   int save_id() const { return info_->save_id; }
   int render_process_id() const { return info_->render_process_id; }
   int render_view_id() const { return info_->render_view_id; }
   int request_id() const { return info_->request_id; }
   SaveFileCreateInfo::SaveFileSource save_source() const {
     return info_->save_source;
   }
 
  private:
+  BaseFile file_;
   scoped_ptr<const SaveFileCreateInfo> info_;
 
   DISALLOW_COPY_AND_ASSIGN(SaveFile);
 };
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_SAVE_FILE_H_