OS_MAC should be OS_MACOSX.

chrome/browser/download/download_file.cc

 // Copyright (c) 2006-2008 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.h"
 
 #include "base/file_util.h"
 #include "base/path_service.h"
 #include "base/scoped_ptr.h"
 #include "base/string_util.h"
@@ skipping 119 matching lines @@
   DCHECK(!full_path_.empty());
   file_ = file_util::OpenFile(full_path_, open_mode);
   if (!file_) {
     return false;
   }
 
 #if defined(OS_WIN)
   // Sets the Zone to tell Windows that this file comes from the internet.
   // We ignore the return value because a failure is not fatal.
   win_util::SetInternetZoneIdentifier(full_path_);
-#elif defined(OS_MAC)
+#elif defined(OS_MACOSX)
   // TODO(port) there should be an equivalent on Mac (there isn't on Linux).
   NOTREACHED();
 #endif
   return true;
 }
 
 // DownloadFileManager implementation ------------------------------------------
 
 DownloadFileManager::DownloadFileManager(MessageLoop* ui_loop,
                                          ResourceDispatcherHost* rdh)
@@ skipping 444 matching lines @@
     ui_loop_->PostTask(FROM_HERE, NewRunnableMethod(
         this, &DownloadFileManager::StopUpdateTimer));
 }
 
 // static
 void DownloadFileManager::DeleteFile(const FilePath& path) {
   // Make sure we only delete files.
   if (!file_util::DirectoryExists(path))
     file_util::Delete(path, false);
 }