Add a visitor for Elements

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index 8269768c04977e5bd78d0827747763a0522bc562..67e87a3a2a1df51d17a4b18aadccf6b89b700265 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -19,7 +19,8 @@ import 'parser_helper.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/elements/modelx.dart'
     show ElementX,
          LibraryElementX,
-         ErroneousElementX;
+         ErroneousElementX,
+         FunctionElementX;
 
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
     hide TreeElementMapping;
@@ -394,7 +395,8 @@ class MockCompiler extends Compiler {
 
   resolverVisitor() {
     Element mockElement =
-        new ElementX('', ElementKind.FUNCTION, mainApp.entryCompilationUnit);
+      new FunctionElementX('', ElementKind.FUNCTION, Modifiers.EMPTY,
+                           mainApp.entryCompilationUnit, false);
     ResolverVisitor visitor =
         new ResolverVisitor(this, mockElement,
                             new CollectingTreeElements(mockElement));