Make pnacl install on demand when it is not already installed.

chrome/browser/component_updater/pnacl/pnacl_component_installer.h

 // Copyright (c) 2011 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_COMPONENT_UPDATER_PNACL_PNACL_COMPONENT_INSTALLER_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_PNACL_PNACL_COMPONENT_INSTALLER_H_
 
+#include "base/callback_forward.h"
+
 class ComponentUpdateService;
 class Version;
 
 namespace base {
 class DictionaryValue;
 }
 
 // Component update registration for Portable Native Client.
 void RegisterPnaclComponent(ComponentUpdateService* cus);
 
 // Returns true if this browser is compatible with the given Pnacl component
 // manifest, with the version specified in the manifest in |version_out|.
 bool CheckPnaclComponentManifest(base::DictionaryValue* manifest,
                                  Version* version_out);
 
+// Ask the given component update service to check for an update.
+// The |installed| callback will be run with |true| on success,
+// or run with |false| on an error.
+// The callback is called on the UI thread.
+void CheckUpdatesForPnacl(ComponentUpdateService* cus,
+                          const base::Callback<void(bool)>& installed);
+
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_PNACL_PNACL_COMPONENT_INSTALLER_H_