Diagnose unbalanced parentheses better.

dart/sdk/lib/_internal/compiler/implementation/scanner/token.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.
 
 part of scanner;
 
 const int EOF_TOKEN = 0;
 
 const int KEYWORD_TOKEN = $k;
 const int IDENTIFIER_TOKEN = $a;
@@ skipping 123 matching lines @@
   String toString() => info.value.toString();
 
   /**
    * The text parsed by this token.
    */
   String slowToString() => toString();
 
   /**
    * The number of characters parsed by this token.
    */
-  int get slowCharCount => slowToString().length;
+  int get slowCharCount {
+    if (info == BAD_INPUT_INFO) {
+      // This is a token that wraps around an error message. Return 1
+      // instead of the size of the length of the error message.
+      return 1;
+    } else {
+      return slowToString().length;
+    }
+  }
 }
 
 /**
  * A keyword token.
  */
 class KeywordToken extends Token {
   final Keyword value;
   String get stringValue => value.syntax;
 
   KeywordToken(Keyword value, int charOffset)
@@ skipping 340 matching lines @@
 
 const PrecedenceInfo HEXADECIMAL_INFO =
   const PrecedenceInfo(const SourceString('hexadecimal'), 0, HEXADECIMAL_TOKEN);
 
 const PrecedenceInfo COMMENT_INFO =
   const PrecedenceInfo(const SourceString('comment'), 0, COMMENT_TOKEN);
 
 // For reporting lexical errors.
 const PrecedenceInfo ERROR_INFO =
   const PrecedenceInfo(const SourceString('?'), 0, UNKNOWN_TOKEN);