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

chrome/browser/extensions/app_host_installer.h

Index: chrome/browser/extensions/app_host_installer.h
diff --git a/chrome/browser/extensions/app_host_installer.h b/chrome/browser/extensions/app_host_installer.h
new file mode 100644
index 0000000000000000000000000000000000000000..9a52bc97bad59537a9cb677d5df119883db11498
--- /dev/null
+++ b/chrome/browser/extensions/app_host_installer.h
@@ -0,0 +1,28 @@
+// 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_H_
+#define CHROME_BROWSER_EXTENSIONS_APP_HOST_INSTALLER_H_
+
+#include "base/callback_forward.h"
+
+namespace extensions {
+
+class Extension;
+
+namespace app_host_installer {
+
+// Installs the App Host if it is absent, but is required for the given
+// extension on the current platform.
+// Calls |completion_callback| on the original calling thread after checks
+// and (possible) installation are complete, with a boolean that will be false
+// iff the installation was required but failed.
+void InstallAppHostIfNecessary(const Extension& extension,
+    const base::Callback<void(bool)>& completion_callback);
+
+}  // namespace app_host_installer
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_APP_HOST_INSTALLER_H_