If Chrome Binaries version > App Host version, then update App Host.

chrome/browser/extensions/app_host/app_host_upgrade.h

Index: chrome/browser/extensions/app_host/app_host_upgrade.h
diff --git a/chrome/browser/extensions/app_host/app_host_upgrade.h b/chrome/browser/extensions/app_host/app_host_upgrade.h
new file mode 100755
index 0000000000000000000000000000000000000000..aeb82ab7787a4cde6d908564ed9c7cb4232ae5b1
--- /dev/null
+++ b/chrome/browser/extensions/app_host/app_host_upgrade.h
@@ -0,0 +1,29 @@
+// 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_APP_HOST_UPGRADE_H_
+#define CHROME_BROWSER_EXTENSIONS_APP_HOST_APP_HOST_UPGRADE_H_
+
+#include "base/version.h"

[erikwright (departed), 2012/09/13 01:13:44]

forward declare Version instead.

[huangs, 2012/09/13 04:40:47]

Done.

+
+namespace app_host {
+
+extern const wchar_t kMultiInstallAppGuid[];
+extern const wchar_t kChromeAppHostAppGuid[];
+
+// Fetches the app version ("pv" entry) of a Google product, given the
+// app GUID ("{###...###}") and the installation level.
+// Returns: true if successful.
+bool GetAppVersionForInstallationLevel(const wchar_t* app_guid,
+                                       bool system_level,
+                                       Version* version);
+
+// Calls setup.exe to reinstall App Host, using setup.exe for the
+// specified installation level.
+// Returns: true if successful.
+bool UpgradeAppHost(bool system_level);
+
+}  // namespace app_host
+
+#endif  // CHROME_BROWSER_EXTENSIONS_APP_HOST_APP_HOST_UPGRADE_H_