Use closure conversion in new dart2js backend.

pkg/compiler/lib/src/dart_backend/backend_ast_emitter.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 backend_ast_emitter;
 
 import '../tree_ir/tree_ir_nodes.dart' as tree;
 import 'backend_ast_nodes.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
@@ skipping 876 matching lines @@
 
   @override
   Expression visitSuperInitializer(tree.SuperInitializer node,
                                    BuilderContext<Statement> context) {
     List<Argument> arguments = node.arguments.map((tree.Statement argument) {
       return ensureExpression(buildInInitializerContext(argument, context));
     }).toList();
     return new SuperInitializer(node.target,
                                 emitArguments(arguments, node.selector));
   }
+
+  @override
+  visitGetField(tree.GetField node, arg) => errorUnsupportedNode(node);
+
+  @override
+  visitSetField(tree.SetField node, arg) => errorUnsupportedNode(node);
+
+  @override
+  visitCreateBox(tree.CreateBox node, arg) => errorUnsupportedNode(node);
+
+  @override
+  visitCreateClosureClass(tree.CreateClosureClass node, arg) {
+    return errorUnsupportedNode(node);
+  }
+
+  errorUnsupportedNode(tree.JsSpecificNode node) {
+    throw '$node not supported by dart backend';
+  }
 }
 
 class TypeGenerator {
 
   /// TODO(johnniwinther): Remove this when issue 21283 has been resolved.
   static int pseudoNameCounter = 0;
 
   static Parameter emitParameter(DartType type,
                                  BuilderContext<Statement> context,
                                  {String name,
@@ skipping 329 matching lines @@
       : super(name, ElementKind.VARIABLE, enclosingElement, variables, null);
 
   ExecutableElement get executableContext => enclosingElement;
 
   ExecutableElement get memberContext => executableContext.memberContext;
 
   bool get isLocal => true;
 
   LibraryElement get implementationLibrary => enclosingElement.library;
 }