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

pkg/front_end/lib/src/fasta/parser/parser.dart

 // Copyright (c) 2012, 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.parser.parser;
 
 import '../scanner.dart' show ErrorToken;
 
 import '../scanner/recover.dart' show closeBraceFor, skipToEof;
 
@@ skipping 883 matching lines @@
   Token expect(String string, Token token) {
     if (!identical(string, token.stringValue)) {
       return reportUnrecoverableError(
           token, ErrorKind.ExpectedButGot, {"expected": string})?.next;
     }
     return token.next;
   }
 
   Token parseTypeVariable(Token token) {
     listener.beginTypeVariable(token);
+    token = parseMetadataStar(token);
     token = parseIdentifier(token, IdentifierContext.typeVariableDeclaration);
     Token extendsOrSuper = null;
     if (optional('extends', token) || optional('super', token)) {
       extendsOrSuper = token;
       token = parseType(token.next);
     } else {
       listener.handleNoType(token);
     }
     listener.endTypeVariable(token, extendsOrSuper);
     return token;
@@ skipping 2690 matching lines @@
         break;
     }
     if (isRecoverable) {
       listener.handleRecoverableError(token, kind, arguments);
       return null;
     } else {
       return listener.handleUnrecoverableError(token, kind, arguments);
     }
   }
 }