More work on ContextBuilder

pkg/analyzer/lib/context/declared_variables.dart

Index: pkg/analyzer/lib/context/declared_variables.dart
diff --git a/pkg/analyzer/lib/context/declared_variables.dart b/pkg/analyzer/lib/context/declared_variables.dart
index 9a0322cd4a0ca019d1254eae36639c7a7224bc75..86d6234b436e586d238eb22cc2f0690a237dab8d 100644
--- a/pkg/analyzer/lib/context/declared_variables.dart
+++ b/pkg/analyzer/lib/context/declared_variables.dart
@@ -23,6 +23,11 @@ class DeclaredVariables {
   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) {