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

chrome/browser/download/download_file_picker.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 "chrome/browser/download/download_file_picker.h"
 
 #include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/platform_util.h"
 #include "chrome/browser/profiles/profile.h"
 #include "content/browser/download/save_package.h"
 #include "content/browser/tab_contents/tab_contents.h"
 #include "grit/generated_resources.h"
 #include "ui/base/l10n/l10n_util.h"
 
 DownloadFilePicker::DownloadFilePicker(
-    DownloadManager* download_manager,
+    DownloadManagerInterface* download_manager,
     TabContents* tab_contents,
     const FilePath& suggested_path,
     void* params)
     : download_manager_(download_manager) {
   select_file_dialog_ = SelectFileDialog::Create(this);
   SelectFileDialog::FileTypeInfo file_type_info;
   FilePath::StringType extension = suggested_path.Extension();
   if (!extension.empty()) {
     extension.erase(extension.begin());  // drop the .
     file_type_info.extensions.resize(1);
@@ skipping 26 matching lines @@
   if (download_manager_)
     download_manager_->FileSelected(path, params);
   delete this;
 }
 
 void DownloadFilePicker::FileSelectionCanceled(void* params) {
   if (download_manager_)
     download_manager_->FileSelectionCanceled(params);
   delete this;
 }