Emit a compile-time error when the name of a variable is referenced in the

sdk/lib/_internal/compiler/implementation/resolution/scope.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 resolution;
 
 abstract class Scope {
   /**
    * Adds [element] to this scope. This operation is only allowed on mutable
    * scopes such as [MethodScope] and [BlockScope].
@@ skipping 23 matching lines @@
   }
 
   Element localLookup(SourceString name);
 
   static Scope buildEnclosingScope(Element element) {
     return element.enclosingElement != null
         ? element.enclosingElement.buildScope() : element.buildScope();
   }
 }
 
+class VariableDefinitionScope extends NestedScope {
+  final SourceString variableName;
+  bool variableReferencedInInitializer = false;
+
+  VariableDefinitionScope(Scope parent, this.variableName) : super(parent);
+
+  Element localLookup(SourceString name) {
+    if (name == variableName) {
+      variableReferencedInInitializer = true;
+    }
+    return null;
+  }
+
+  Element add(Element newElement) {
+    throw "Cannot add element to VariableDefinitionScope";
+  }
+}
+
 /**
  * [TypeDeclarationScope] defines the outer scope of a type declaration in
  * which the declared type variables and the entities in the enclosing scope are
  * available but where declared and inherited members are not available. This
  * scope is only used for class declarations during resolution of the
  * class hierarchy. In all other cases [ClassScope] is used.
  */
 class TypeDeclarationScope extends NestedScope {
   final TypeDeclarationElement element;
 
@@ skipping 100 matching lines @@
 
   Element localLookup(SourceString name) => library.find(name);
   Element lookup(SourceString name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element to a library scope";
   }
 
   String toString() => 'LibraryScope($library)';
 }