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

chrome/browser/download/download_prefs.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_prefs.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/string_split.h"
@@ skipping 76 matching lines @@
     if (download_util::DownloadPathIsDangerous(current_download_dir)) {
       prefs->SetFilePath(prefs::kDownloadDefaultDirectory,
                          default_download_path);
     }
     prefs->SetBoolean(prefs::kDownloadDirUpgraded, true);
   }
 }
 
 // static
 DownloadPrefs* DownloadPrefs::FromDownloadManager(
-    DownloadManager* download_manager) {
+    DownloadManagerInterface* download_manager) {
   ChromeDownloadManagerDelegate* delegate =
       static_cast<ChromeDownloadManagerDelegate*>(download_manager->delegate());
   return delegate->download_prefs();
 }
 
 bool DownloadPrefs::PromptForDownload() const {
   // If the DownloadDirectory policy is set, then |prompt_for_download_| should
   // always be false.
   DCHECK(!download_path_.IsManaged() || !prompt_for_download_.GetValue());
   return *prompt_for_download_;
@@ skipping 55 matching lines @@
     extensions.erase(extensions.size() - 1);
 
   prefs_->SetString(prefs::kDownloadExtensionsToOpen, extensions);
 }
 
 bool DownloadPrefs::AutoOpenCompareFunctor::operator()(
     const FilePath::StringType& a,
     const FilePath::StringType& b) const {
   return FilePath::CompareLessIgnoreCase(a, b);
 }