Complain about assignments to parenthesized expressions.

pkg/front_end/lib/src/fasta/scanner/array_based_scanner.dart

 // Copyright (c) 2011, 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.scanner.array_based_scanner;
 
 import 'error_token.dart' show ErrorToken;
 
 import 'keyword.dart' show Keyword;
 
-import 'precedence.dart' show EOF_INFO, PrecedenceInfo;
+import 'precedence.dart' show PrecedenceInfo;
 
 import 'token.dart'
     show
         BeginGroupToken,
         CommentToken,
         DartDocToken,
         KeywordToken,
         StringToken,
         SymbolToken,
         Token;
@@ skipping 291 matching lines @@
    * something which cannot possibly be part of a type parameter/argument
    * list, like the '=' in the above example.
    */
   void discardOpenLt() {
     while (!groupingStack.isEmpty &&
         identical(groupingStack.head.kind, LT_TOKEN)) {
       groupingStack = groupingStack.tail;
     }
   }
 }