Handle escapes in string literals.

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(() {
       Link<Element> elements = scanElements(compilationUnit);
       for (Link<Element> link = elements; !link.isEmpty(); link = link.tail) {
         Element existing = compiler.universe.find(link.head.name);
         if (existing !== null) {
           // TODO(ahe): Is this the right place to handle this?
           compiler.cancel('Duplicate definition',
                           token: link.head.dynamic.beginToken);
         }
         compiler.universe.define(link.head);
       }
     });
   }
 
   Link<Element> scanElements(CompilationUnitElement compilationUnit) {
     Script script = compilationUnit.script;
-    Token tokens = new StringScanner(script.text).tokenize();
+    Token tokens;
+    try {
+      tokens = new StringScanner(script.text).tokenize();
+    } catch (MalformedInputException e) {
+      if (e.message is int) {
+        Token token = new Token(ERROR_INFO, e.message);
+        compiler.cancel('Unexpected character', token: token);
+        throw "Unrecoverable error";
+      }
+    }
     ElementListener listener = new ElementListener(compiler, compilationUnit);
     PartialParser parser = new PartialParser(listener);
     parser.parseUnit(tokens);
     return listener.topLevelElements;
   }
 }