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

content/shell/shell_download_manager_delegate.cc

 // 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.
 
 #include "content/shell/shell_download_manager_delegate.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <commdlg.h>
 #endif
@@ skipping 54 matching lines @@
           &ShellDownloadManagerDelegate::GenerateFilename,
           this, download_id, state, generated_name));
   return false;
 }
 
 void ShellDownloadManagerDelegate::GenerateFilename(
     int32 download_id,
     DownloadStateInfo state,
     const FilePath& generated_name) {
   if (state.suggested_path.empty()) {
-    state.suggested_path = download_manager_->browser_context()->GetPath().
+    state.suggested_path = download_manager_->BrowserContext()->GetPath().
         Append(FILE_PATH_LITERAL("Downloads"));
     if (!file_util::PathExists(state.suggested_path))
       file_util::CreateDirectory(state.suggested_path);
   }
 
   state.suggested_path = state.suggested_path.Append(generated_name);
 
   BrowserThread::PostTask(
       BrowserThread::UI,
       FROM_HERE,
@@ skipping 114 matching lines @@
 void ShellDownloadManagerDelegate::ChooseSavePath(
     const base::WeakPtr<SavePackage>& save_package,
     const FilePath& suggested_path,
     bool can_save_as_complete) {
 }
 
 void ShellDownloadManagerDelegate::DownloadProgressUpdated() {
 }
 
 }  // namespace content