Implement metadata on classes and additional semantic checks.

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

Index: pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart b/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
index 2efe75377ad5f9d90542f75b172f7cd16952b02b..fe46212c634eb8a0f43ccbc43b0699dfabf4a83a 100644
--- a/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/modifier_builder.dart
@@ -36,4 +36,10 @@ abstract class ModifierBuilder extends Builder {
   bool get isNamedMixinApplication {
     return (modifiers & namedMixinApplicationMask) != 0;
   }
+
+  bool get isClassMember => false;
+
+  String get name;
+
+  bool get isNative => false;
 }