Add TypeUse.

pkg/compiler/lib/src/resolution/variables.dart

Index: pkg/compiler/lib/src/resolution/variables.dart
diff --git a/pkg/compiler/lib/src/resolution/variables.dart b/pkg/compiler/lib/src/resolution/variables.dart
index 5cf5f4b2a160d6e8e2fce0e87111a728abe85802..6f22eed3214167ac8b1f69657f4b30f15930e2b8 100644
--- a/pkg/compiler/lib/src/resolution/variables.dart
+++ b/pkg/compiler/lib/src/resolution/variables.dart
@@ -11,6 +11,8 @@ import '../elements/modelx.dart' show
     LocalVariableElementX,
     VariableList;
 import '../tree/tree.dart';
+import '../universe/use.dart' show
+    TypeUse;
 import '../util/util.dart' show
     Link;
 
@@ -54,7 +56,9 @@ class VariableDefinitionsVisitor extends CommonResolverVisitor<Identifier> {
 
   Identifier visitIdentifier(Identifier node) {
     // The variable is initialized to null.
-    registry.registerInstantiatedType(compiler.coreTypes.nullType);
+    // TODO(johnniwinther): Register a feature instead.
+    registry.registerTypeUse(
+        new TypeUse.instantiation(compiler.coreTypes.nullType));
     if (definitions.modifiers.isConst) {
       reporter.reportErrorMessage(
           node, MessageKind.CONST_WITHOUT_INITIALIZER);