Implement is-checks against type variables.

sdk/lib/_internal/compiler/implementation/enqueue.dart

Index: sdk/lib/_internal/compiler/implementation/enqueue.dart
diff --git a/sdk/lib/_internal/compiler/implementation/enqueue.dart b/sdk/lib/_internal/compiler/implementation/enqueue.dart
index 18b448d7443e256fa201b99dd6a0648cfa68cfca..acf846242ac4f9f16e459199f907fa3f0f9d001a 100644
--- a/sdk/lib/_internal/compiler/implementation/enqueue.dart
+++ b/sdk/lib/_internal/compiler/implementation/enqueue.dart
@@ -86,6 +86,11 @@ abstract class Enqueuer {
   // the work list'?
   bool addElementToWorkList(Element element, [TreeElements elements]);
 
+  void registerInstantiatedType(InterfaceType type) {
+    universe.instantiatedTypes.add(type);
+    registerInstantiatedClass(type.element);
+  }
+
   void registerInstantiatedClass(ClassElement cls) {
     if (universe.instantiatedClasses.contains(cls)) return;
     if (!cls.isAbstract(compiler)) {