Make application shortcuts point to app_host.exe, install App Host during app installation.

chrome/browser/extensions/app_host_installer_impl_win.h

+// Copyright (c) 2012 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_EXTENSIONS_APP_HOST_INSTALLER_IMPL_WIN_H_
+#define CHROME_BROWSER_EXTENSIONS_APP_HOST_INSTALLER_IMPL_WIN_H_
+
+#include "base/basictypes.h"
+#include "base/callback_forward.h"
+#include "base/win/object_watcher.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace extensions {
+
+class Extension;
+
+namespace app_host_installer {
+
+using content::BrowserThread;
+
+// Determines if the App Host is installed and, if not, installs it.
+class AppHostInstallerImpl {
+ public:
+  // Asynchronously checks the system state and installs the App Host if not
+  // present. |completion_callback| will be notified on the caller's thread
+  // when the installation process completes. No timeout is used - thus
+  // |completion_callback| may be held for an arbitrarily long time,
+  // including past browser shutdown.
+  static void EnsureAppHostInstalled(
+      const base::Callback<void(bool)>& completion_callback);
+
+ private:
+  AppHostInstallerImpl(const base::Callback<void(bool)>& completion_callback,

[erikwright (departed), 2012/10/09 21:51:52]

// Constructs an AppHostInstallerImpl which will call |completion_callback| on
the specified thread upon installation completion.

[huangs, 2012/10/09 22:44:26]

Done.

+                       BrowserThread::ID caller_thread_id);
+
+  ~AppHostInstallerImpl();
+
+  // Checks the system state on the FILE thread. Will trigger InstallAppHost()
+  // if App Host is not installed.
+  void EnsureAppHostInstalledInternal();
+
+  // Runs on the FILE thread. Installs App Host.
+  void InstallAppHost();
+
+  // Passes |success| to |completion_callback| on the original caller thread.
+  // Deletes the AppHostInstallerImpl.
+  void Finish(bool success);
+
+  // Callback that should be invoked on install completion on the caller thread.

[erikwright (departed), 2012/10/09 21:51:52]

My personal opinion is that comments are unnecessary and possibly reduce
readability for the private member variables.

I will defer to Ben's opinion, though.

[huangs, 2012/10/09 22:44:26]

Okay, I'll wait.  I realized that crx_installer.h has a bunch of comments, so I
decide to imitate.

[benwells, 2012/10/10 03:22:04]

I agree with Erik, commenting private member variables adds noise and has a
tendency to mislead over time. If the variables are well named it is
unnecessary. So, feel free to remove the comments :)

[huangs, 2012/10/10 14:39:49]

Done.

+  base::Callback<void(bool)> completion_callback_;
+
+  // The caller thread that |completion_callback_| should be called on.
+  BrowserThread::ID caller_thread_id_;
+
+  // The process handle of the command to install App Host.
+  base::win::ScopedHandle process_;
+
+  // The delegate to be signaled when |process_| completes.
+  scoped_ptr<base::win::ObjectWatcher::Delegate> delegate_;
+
+  // Watcher for |process_|.
+  base::win::ObjectWatcher watcher_;
+
+ DISALLOW_COPY_AND_ASSIGN(AppHostInstallerImpl);
+};
+
+}  // namespace app_host_installer
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_APP_HOST_INSTALLER_IMPL_WIN_H_