Rename the inner function of async functions.

tests/compiler/dart2js/async_await_js_transform_test.dart

 // Copyright (c) 2015, 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.
 
 import "package:expect/expect.dart";
 import "package:compiler/src/js/js.dart";
 import "package:compiler/src/js/rewrite_async.dart";
 
 import "backend_dart/dart_printer_test.dart" show PrintDiagnosticListener;
 
 void testTransform(String source, String expected) {
   Fun fun = js(source);
   Fun rewritten = new AsyncRewriter(
       null, // The diagnostic helper should not be used in these tests.
       null,
       asyncHelper: new VariableUse("thenHelper"),
       newCompleter: new VariableUse("Completer"),
-      safeVariableName: (String name) => "__$name").rewrite(fun);
+      safeVariableName: (String name) => "__$name",
+      bodyName: "body").rewrite(fun);
 
   JavaScriptPrintingOptions options = new JavaScriptPrintingOptions();
   SimpleJavaScriptPrintingContext context =
       new SimpleJavaScriptPrintingContext();
   Printer printer = new Printer(options, context);
   printer.visit(rewritten);
   Expect.stringEquals(expected, context.getText());
 }
 
 main() {
@@ skipping 1103 matching lines @@
           // implicit return
           return thenHelper(null, 0, __completer, null);
         case 1:
           // rethrow
           return thenHelper(__currentError, 1, __completer);
       }
   }
   return thenHelper(null, __body, __completer, null);
 }""");
 }