Diagnose unterminated "grouping" characters.

dart/frog/leg/scanner/scanner_task.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.
 
 class ScannerTask extends CompilerTask {
   ScannerTask(Compiler compiler) : super(compiler);
   String get name() => 'Scanner';
 
   void scan(CompilationUnitElement compilationUnit) {
     measure(() {
@@ skipping 11 matching lines @@
   }
 
   Link<Element> scanElements(CompilationUnitElement compilationUnit) {
     Script script = compilationUnit.script;
     Token tokens;
     try {
       tokens = new StringScanner(script.text).tokenize();
     } catch (MalformedInputException ex) {
       Token token;
       var message;
-      if (ex.message is int) {
-        token = new Token(EOF_INFO, ex.message);
-        message = 'unexpected character';
+      if (ex.position is num) {
+        // TODO(ahe): Always use tokens in MalformedInputException.
+        token = new Token(EOF_INFO, ex.position);
       } else {
-        token = new Token(EOF_INFO, 0);
-        message = ex.message;
+        token = ex.position;
       }
-      compiler.cancel(message, token: token);
+      compiler.cancel(ex.message, token: token);
     }
     ElementListener listener = new ElementListener(compiler, compilationUnit);
     PartialParser parser = new PartialParser(listener);
     parser.parseUnit(tokens);
     return listener.topLevelElements;
   }
 }