Mark the local for this as used if a constructor call needs type variables.

lib/compiler/implementation/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(TypeAnnotation annotation);
 }
 
@@ skipping 1529 matching lines @@
     world.registerInstantiatedClass(cls);
     cls.forEachInstanceField(
         includeBackendMembers: false,
         includeSuperMembers: true,
         f: (ClassElement enclosingClass, Element member) {
           world.addToWorkList(member);
         });
     return null;
   }
 
-  TypeAnnotation getTypeAnnotationFromSend(Send send) {
-    if (send.selector.asTypeAnnotation() !== null) {
-      return send.selector;
-    } else if (send.selector.asSend() !== null) {
-      Send selector = send.selector;
-      if (selector.receiver.asTypeAnnotation() !== null) {
-        return selector.receiver;
-      }
-    } else {
-      compiler.internalError("malformed send in new expression");
-    }
-  }
-
   /**
    * Try to resolve the constructor that is referred to by [node].
    * Note: this function may return an ErroneousFunctionElement instead of
    * [null], if there is no corresponding constructor, class or library.
    */
   FunctionElement resolveConstructor(NewExpression node) {
     // Resolve the constructor that [node] refers to.
     ConstructorResolver visitor =
         new ConstructorResolver(compiler, this, node.isConst());
     FunctionElement constructor = node.accept(visitor);
     // Try to resolve the type that the new-expression constructs.
-    TypeAnnotation annotation = getTypeAnnotationFromSend(node.send);
+    TypeAnnotation annotation = node.send.getTypeAnnotation();
     if (Element.isInvalid(constructor)) {
       // Resolve the type arguments. We cannot create a type and check the
       // number of type arguments for this annotation, because we do not know
       // the element.
       Link arguments = const EmptyLink<Node>();
       if (annotation.typeArguments != null) {
         arguments = annotation.typeArguments.nodes;
       }
       for (Node argument in arguments) {
         resolveTypeRequired(argument);
@@ skipping 1052 matching lines @@
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) {
     return library.find(name);
   }
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }