Handle metadata in the magic [^] property of class descriptions correctly.

sdk/lib/_internal/compiler/implementation/js_emitter/reflection_data_parser.dart

 // Copyright (c) 2013, 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.
 
 part of dart2js.js_emitter;
 
 // TODO(ahe): Share these with js_helper.dart.
 const FUNCTION_INDEX = 0;
 const NAME_INDEX = 1;
 const CALL_NAME_INDEX = 2;
@@ skipping 221 matching lines @@
 //
 // The entries of [data] are built in [assembleProgram] above.
 
     var name = data[0];
     var uri = data[1];
     var metadata = data[2];
     var globalObject = data[3];
     var descriptor = data[4];
     var isRoot = !!data[5];
     var fields = descriptor && descriptor["${namer.classDescriptorProperty}"];
+    if (fields instanceof Array) fields = fields[0];
     var classes = [];
     var functions = [];
     processStatics(descriptor);
     libraries.push([name, uri, classes, functions, metadata, fields, isRoot,
                     globalObject]);
   }
 ''';
 
   return js('''
 (function (reflectionData) {
@@ skipping 121 matching lines @@
 (function() {
   var result = $array[$index];
   if ($check) {
     throw new Error(
         name + ": expected value of type \'$type\' at index " + ($index) +
         " but got " + (typeof result));
   }
   return result;
 })()''';
 }