Re-land "Add support for metadata on type variables to Fasta parser." (with fixes).

pkg/front_end/lib/src/fasta/source/outline_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.outline_builder;
 
 import 'package:kernel/ast.dart' show AsyncMarker, ProcedureKind;
 
 import '../parser/parser.dart' show FormalParameterType, optional;
 
@@ skipping 554 matching lines @@
     int modifiers = Modifier.validate(pop());
     List<MetadataBuilder> metadata = pop();
     library.addFields(metadata, modifiers, type, names);
   }
 
   @override
   void endTypeVariable(Token token, Token extendsOrSuper) {
     debugEvent("endTypeVariable");
     TypeBuilder bound = pop();
     String name = pop();
+    // TODO(paulberry): type variable metadata should not be ignored.  See
+    // dartbug.com/28981.
+    /* List<MetadataBuilder> metadata = */ pop();
     push(library.addTypeVariable(name, bound, token.charOffset));
   }
 
   @override
   void endPartOf(Token partKeyword, Token semicolon) {
     debugEvent("endPartOf");
     String name = pop();
     List<MetadataBuilder> metadata = pop();
     library.addPartOf(metadata, name);
   }
@@ skipping 115 matching lines @@
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!isDartLibrary || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }