Implement top-level getters.

dart/sdk/lib/_internal/compiler/implementation/closure.dart

Index: dart/sdk/lib/_internal/compiler/implementation/closure.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/closure.dart b/dart/sdk/lib/_internal/compiler/implementation/closure.dart
index a10ccbdf821b2f4ac4e77bcc5aae835ec7b7405d..b0061d90dbc3690e801f991b81337856ab7690ee 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/closure.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/closure.dart
@@ -18,7 +18,6 @@ class ClosureNamer {
   }
 }
 
-
 class ClosureTask extends CompilerTask {
   Map<Node, ClosureClassMap> closureMappingCache;
   ClosureNamer namer;
@@ -68,12 +67,26 @@ class ClosureTask extends CompilerTask {
 // TODO(ahe): These classes continuously cause problems.  We need to
 // move these classes to elements/modelx.dart or see if we can find a
 // more general solution.
-class ClosureFieldElement extends ElementX {
+class ClosureFieldElement extends ElementX implements VariableElement {
+  /// The source variable this element refers to.
+  final Element variableElement;
+
   ClosureFieldElement(SourceString name,
                       this.variableElement,
                       ClassElement enclosing)
       : super(name, ElementKind.FIELD, enclosing);
 
+  VariableListElement get variables {
+    throw new SpannableAssertionFailure(
+        variableElement, 'Should not access variables of ClosureFieldElement.');
+  }
+
+  Expression get cachedNode {
+    throw new SpannableAssertionFailure(
+        variableElement,
+        'Should not access cachedNode of ClosureFieldElement.');
+  }
+
   bool isInstanceMember() => true;
   bool isAssignable() => false;
   // The names of closure variables don't need renaming, since their use is very
@@ -86,11 +99,6 @@ class ClosureFieldElement extends ElementX {
   }
 
   String toString() => "ClosureFieldElement($name)";
-
-  /**
-   * The source variable this element refers to.
-   */
-  final Element variableElement;
 }
 
 // TODO(ahe): These classes continuously cause problems.  We need to