Return null from stringValue and call slowToString() instead of toString().

dart/frog/leg/native_handler.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('native');
 #import('leg.dart');
 #import('elements/elements.dart');
 #import('scanner/scannerlib.dart');
 #import('ssa/ssa.dart');
 #import('tree/tree.dart');
@@ skipping 116 matching lines @@
       i++;
     });
     String foreignParameters = Strings.join(arguments, ',');
 
     String methodName = builder.compiler.namer.instanceMethodName(
         element.name, parameters.parameterCount);
 
     HInstruction thenInstruction;
     void visitThen() {
       SourceString jsCode = new SourceString(
-          '$receiver${element.name}($foreignParameters)');
+          '$receiver${element.name.slowToString()}($foreignParameters)');
       thenInstruction =
           new HForeign(jsCode, const SourceString('Object'), inputs);
       builder.add(thenInstruction);
     }
 
     if (!element.isInstanceMember()) {
       // If the method is a non-instance method, we just generate a direct
       // call to the native method.
       visitThen();
       builder.stack.add(thenInstruction);
@@ skipping 44 matching lines @@
 
   } else if (!node.arguments.tail.isEmpty()) {
     builder.compiler.cancel('More than one argument to native');
   } else {
     LiteralString jsCode = node.arguments.head;
     builder.push(new HForeign(builder.unquote(jsCode, 0),
                               const SourceString('Object'),
                               <HInstruction>[]));
   }
 }