Implement metadata on classes and additional semantic checks.

pkg/front_end/lib/src/fasta/builder/modifier_builder.dart

 // Copyright (c) 2016, 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 fasta.modifier_builder;
 
 import '../modifier.dart'
     show
         abstractMask,
         constMask,
@@ skipping 18 matching lines @@
 
   bool get isExternal => (modifiers & externalMask) != 0;
 
   bool get isFinal => (modifiers & finalMask) != 0;
 
   bool get isStatic => (modifiers & staticMask) != 0;
 
   bool get isNamedMixinApplication {
     return (modifiers & namedMixinApplicationMask) != 0;
   }
+
+  bool get isClassMember => false;
+
+  String get name;
+
+  bool get isNative => false;
 }