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

extensions/browser/extension_system.h

Index: extensions/browser/extension_system.h
diff --git a/extensions/browser/extension_system.h b/extensions/browser/extension_system.h
index c6d2e091a50c20b75dbb5239c2c10923fb47d27d..7758051d01d36598e9bf36c937067410a9ceeb48 100644
--- a/extensions/browser/extension_system.h
+++ b/extensions/browser/extension_system.h
@@ -122,6 +122,13 @@ class ExtensionSystem : public KeyedService {
   // so it can be retrieved from ExtensionSystem directly.
   virtual scoped_ptr<ExtensionSet> GetDependentExtensions(
       const Extension* extension) = 0;
+
+  // Install an updated version of |extension_id| with the version given in
+  // temp_dir. Ownership of |temp_dir| in the filesystem is transferred and
+  // implementors of this function are responsible for cleaning it up on
+  // errors, etc.
+  virtual void InstallUpdate(const std::string& extension_id,
+                             const base::FilePath& temp_dir) = 0;
 };
 
 }  // namespace extensions