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

chrome/browser/component_updater/pnacl/pnacl_component_installer.h

Index: chrome/browser/component_updater/pnacl/pnacl_component_installer.h
diff --git a/chrome/browser/component_updater/pnacl/pnacl_component_installer.h b/chrome/browser/component_updater/pnacl/pnacl_component_installer.h
index ffcc3535c07abd0184396b6edd93d81256a96b70..3174551c18680c72e8baf99dd5bc36624d2e0581 100644
--- a/chrome/browser/component_updater/pnacl/pnacl_component_installer.h
+++ b/chrome/browser/component_updater/pnacl/pnacl_component_installer.h
@@ -5,6 +5,8 @@
 #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;
 
@@ -20,4 +22,11 @@ void RegisterPnaclComponent(ComponentUpdateService* cus);
 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_