Don't build a bunch of stuff on Aura, rather than ifdefing out code in it.

chrome/browser/plugin_download_helper.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 CHROME_BROWSER_PLUGIN_DOWNLOAD_HELPER_H_
 #define CHROME_BROWSER_PLUGIN_DOWNLOAD_HELPER_H_
 #pragma once
 
 #include <string>
+
 #include "build/build_config.h"
-
-#if defined(OS_WIN)
 #include "base/file_path.h"
 #include "base/message_loop_proxy.h"
 #include "content/public/common/url_fetcher_delegate.h"
 #include "net/base/file_stream.h"
 #include "net/url_request/url_request.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace net {
 class URLRequestContextGetter;
 }
@@ skipping 34 matching lines @@
   // indicating that the download completed.
   gfx::NativeWindow download_file_caller_window_;
 
   std::string download_url_;
 
   PluginDownloadUrlHelper::DownloadDelegate* delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginDownloadUrlHelper);
 };
 
-#endif  // OS_WIN
-
 #endif  // CHROME_BROWSER_PLUGIN_DOWNLOAD_HELPER_H_