Add support for fields to the new dart backend.

pkg/compiler/lib/src/js_backend/codegen/codegen.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 code_generator;
 
 import 'glue.dart';
 
 import '../../tree_ir/tree_ir_nodes.dart' as tree_ir;
 import '../../js/js.dart' as js;
@@ skipping 78 matching lines @@
       glue.reportInternalError('$node did not produce code.');
     }
     return result;
   }
 
   /// Generates a name for the given variable. First trying with the name of
   /// the [Variable.element] if it is non-null.
   String getVariableName(tree_ir.Variable variable) {
     // TODO(sigurdm): Handle case where the variable belongs to an enclosing
     // function.
-    if (variable.host.element != currentFunction) giveup(variable);
+    if (variable.host != currentFunction) giveup(variable);
 
     // Get the name if we already have one.
     String name = variableNames[variable];
     if (name != null) {
       return name;
     }
 
     // Synthesize a variable name that isn't used elsewhere.
     // The [usedVariableNames] set is shared between nested emitters,
     // so this also prevents clash with variables in an enclosing/inner scope.
@@ skipping 281 matching lines @@
     accumulator.add(
         buildWhile(new js.LiteralBool(true), node.body, node.label, node));
   }
 
   @override
   void visitReturn(tree_ir.Return node) {
     accumulator.add(new js.Return(visitExpression(node.value)));
   }
 
 }