Add extensions code to use common updater in components/update_client/

chrome/browser/extensions/extension_system_impl.h

Index: chrome/browser/extensions/extension_system_impl.h
diff --git a/chrome/browser/extensions/extension_system_impl.h b/chrome/browser/extensions/extension_system_impl.h
index 49369ff807752e92e545d44bbfb954863764b728..0ad9357027c5dffac793bcdc51f3ce81e221ebc2 100644
--- a/chrome/browser/extensions/extension_system_impl.h
+++ b/chrome/browser/extensions/extension_system_impl.h
@@ -54,6 +54,8 @@ class ExtensionSystemImpl : public ExtensionSystem {
   ContentVerifier* content_verifier() override;  // shared
   scoped_ptr<ExtensionSet> GetDependentExtensions(
       const Extension* extension) override;
+  void InstallUpdate(const std::string& extension_id,
+                     const base::FilePath& temp_dir) override;
 
  private:
   friend class ExtensionSystemSharedFactory;