Introduce background Download process to android

content/app/android/download_main.cc

+// Copyright 2016 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 "base/message_loop/message_loop.h"
+#include "base/threading/platform_thread.h"
+#include "content/public/common/main_function_params.h"
+
+namespace content {
+
+// Mainline routine for running as the download process.
+int DownloadMain(const MainFunctionParams& parameters) {
+  // The main message loop of the utility process.
+  base::MessageLoop main_message_loop;
+  base::PlatformThread::SetName("CrDownloadMain");
+  base::MessageLoop::current()->Run();
+
+  return 0;
+}
+
+}  // namespace content