Create type masks lazily.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 860 matching lines @@
     // statement context or an expression context, so we register both
     // here, even though we may not need the throwExpression helper.
     enqueueInResolution(getWrapExceptionHelper(), elements);
     enqueueInResolution(getThrowExpressionHelper(), elements);
   }
 
   void registerLazyField(TreeElements elements) {
     enqueueInResolution(getCyclicThrowHelper(), elements);
   }
 
-  void registerTypeLiteral(Element element, TreeElements elements) {
+  void registerTypeLiteral(Element element,
+                           Enqueuer enqueuer,
+                           TreeElements elements) {
+    enqueuer.registerInstantiatedClass(typeImplementation, elements);
     enqueueInResolution(getCreateRuntimeType(), elements);
     // TODO(ahe): Might want to register [element] as an instantiated class
     // when reflection is used.  However, as long as we disable tree-shaking
     // eagerly it doesn't matter.
     if (element.isTypedef()) {
       typedefTypeLiterals.add(element);
     }
   }
 
   void registerStackTraceInCatch(TreeElements elements) {
@@ skipping 887 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }