Add support for fields to the new dart backend.

pkg/compiler/lib/src/js_backend/codegen/task.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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 
@@ skipping 113 matching lines @@
   void traceGraph(String title, var irObject) {
     if (tracer != null) {
       tracer.traceGraph(title, irObject);
     }
   }
 
   cps.FunctionDefinition compileToCpsIR(AstElement element) {
     // TODO(sigurdm): Support these constructs.
     if (element.isGenerativeConstructorBody ||
         element.enclosingClass is ClosureClassElement ||
-        element.isNative) {
+        element.isNative ||
+        element.isField) {
       giveUp('unsupported element kind: ${element.name}:${element.kind}');
     }
 
     cps.FunctionDefinition cpsNode = irBuilderTask.buildNode(element);
     if (cpsNode == null) {
       giveUp('unable to build cps definition of $element');
     }
     return cpsNode;
   }
 
@@ skipping 10 matching lines @@
 
     // Do not rewrite the IR after variable allocation.  Allocation
     // makes decisions based on an approximation of IR variable live
     // ranges that can be invalidated by transforming the IR.
     new cps.RegisterAllocator().visit(cpsNode);
     return cpsNode;
   }
 
   tree_ir.FunctionDefinition compileToTreeIR(cps.FunctionDefinition cpsNode) {
     tree_builder.Builder builder = new JsBackendTreeBuilder(compiler, glue);
-    tree_ir.FunctionDefinition treeNode = builder.build(cpsNode);
+    tree_ir.FunctionDefinition treeNode = builder.buildFunction(cpsNode);
     assert(treeNode != null);
     traceGraph('Tree builder', treeNode);
     return treeNode;
   }
 
   tree_ir.FunctionDefinition optimizeTreeIR(
       tree_ir.FunctionDefinition treeNode) {
     // Transformations on the Tree IR.
     new StatementRewriter().rewrite(treeNode);
     traceGraph('Statement rewriter', treeNode);
@@ skipping 48 matching lines @@
           new TokenSourceFileLocation(sourceFile, endToken, name);
     }
     return node.withPosition(sourcePosition, endSourcePosition);
   }
 
   SourceFile sourceFileOfElement(Element element) {
     return element.implementation.compilationUnit.script.file;
   }
 
 }