Introduce background Download process to android

content/browser/android/download_process_host.h

+// 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.
+
+#ifndef CONTENT_BROWSER_ANDROID_DOWNLOAD_PROCESS_HOST_H_
+#define CONTENT_BROWSER_ANDROID_DOWNLOAD_PROCESS_HOST_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "content/public/browser/browser_child_process_host.h"
+#include "content/public/browser/browser_child_process_host_delegate.h"
+
+namespace content {
+
+class DownloadProcessHost : public content::BrowserChildProcessHostDelegate {
+ public:

[no sievers, 2016/01/27 00:33:36]

This class is unused.

[qinmin, 2016/01/28 00:58:31]

This is the entry point to create the download process. Moved all the
implementation into child_process_launcher_android, and we no longer need this.
In the future, DownloadControllerAndroidImpl will call startDownloadProcess() to
start the process if it is not created.

+  DownloadProcessHost();
+  ~DownloadProcessHost() override;
+
+  // Starts a process if necessary.  Returns true if it succeeded or a process
+  // has already been started.
+  bool StartProcess();
+
+ private:
+  // content::BrowserChildProcessHostDelegate:
+  bool OnMessageReceived(const IPC::Message& message) override;
+  void OnProcessLaunchFailed() override;
+  void OnProcessCrashed(int exit_code) override;
+  void OnProcessLaunched() override;
+
+  bool started_;
+
+  scoped_ptr<content::BrowserChildProcessHost> process_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadProcessHost);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_ANDROID_DOWNLOAD_PROCESS_HOST_H_