Add ArcEnabled policy implementation

components/arc/arc_service_manager.h

Index: components/arc/arc_service_manager.h
diff --git a/components/arc/arc_service_manager.h b/components/arc/arc_service_manager.h
index b3a1a6d747e449d813fc184697ae8231246ea024..5c36f568fe5c20ce42076f6d8bc263a83d9b2980 100644
--- a/components/arc/arc_service_manager.h
+++ b/components/arc/arc_service_manager.h
@@ -38,6 +38,10 @@ class ArcServiceManager {
   // Called when the main profile is initialized after user logs in.
   void OnPrimaryUserProfilePrepared(const AccountId& account_id);
 
+  // Set ArcBridgeService instance for testing. Call before ArcServiceManager
+  // creation. ArcServiceManager owns |arc_bridge_service|.
+  static void SetArcBridgeServiceForTesting(
+      scoped_ptr<ArcBridgeService> arc_bridge_service);
  private:
   base::ThreadChecker thread_checker_;
   scoped_ptr<ArcBridgeService> arc_bridge_service_;