Remove string constants from Types class.

dart/lib/compiler/implementation/elements/elements.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.
 
 #library('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 662 matching lines @@
 class SynthesizedConstructorElement extends FunctionElement {
   SynthesizedConstructorElement(Element enclosing)
     : super(enclosing.name, ElementKind.GENERATIVE_CONSTRUCTOR,
             null, enclosing);
 
   Token position() => enclosingElement.position();
 }
 
 class VoidElement extends Element {
   VoidElement(Element enclosing)
-      : super(Types.VOID, ElementKind.VOID, enclosing);
+      : super(const SourceString('void'), ElementKind.VOID, enclosing);
   Type computeType(compiler) => compiler.types.voidType;
   Node parseNode(_) {
     throw 'internal error: parseNode on void';
   }
   bool impliesType() => true;
 }
 
 class ClassElement extends ContainerElement {
   final int id;
   Type type;
@@ skipping 365 matching lines @@
   final Node node;
   Type bound;
   Type type;
   TypeVariableElement(name, Element enclosing, this.node, this.type,
                       [this.bound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
   Type computeType(compiler) => type;
   Node parseNode(compiler) => node;
   toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 }