More work on ContextBuilder

pkg/analyzer/lib/context/declared_variables.dart

 // Copyright (c) 2014, 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 analyzer.context.declared_variables;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/src/dart/constant/value.dart';
 import 'package:analyzer/src/generated/resolver.dart' show TypeProvider;
 
 /**
  * An object used to provide access to the values of variables that have been
  * defined on the command line using the `-D` option.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 class DeclaredVariables {
   /**
    * A table mapping the names of declared variables to their values.
    */
   HashMap<String, String> _declaredVariables = new HashMap<String, String>();
 
   /**
+   * Return the names of the variables for which a value has been defined.
+   */
+  Iterable<String> get variableNames => _declaredVariables.keys;
+
+  /**
    * Define a variable with the given [name] to have the given [value].
    */
   void define(String name, String value) {
     _declaredVariables[name] = value;
   }
 
   /**
    * Return the value of the variable with the given [name] interpreted as a
    * 'boolean' value. If the variable is not defined (or [name] is `null`), a
    * DartObject representing "unknown" is returned. If the value cannot be
@@ skipping 43 matching lines @@
    */
   DartObject getString(TypeProvider typeProvider, String name) {
     String value = _declaredVariables[name];
     if (value == null) {
       return new DartObjectImpl(
           typeProvider.stringType, StringState.UNKNOWN_VALUE);
     }
     return new DartObjectImpl(typeProvider.stringType, new StringState(value));
   }
 }