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

dart/frog/leg/emitter.dart

Index: dart/frog/leg/emitter.dart
diff --git a/dart/frog/leg/emitter.dart b/dart/frog/leg/emitter.dart
index e91aa7098e7dc2a107cd31362251d041c8f475ec..e85b81a4d49ad6d3d820fb7755692192d9404653 100644
--- a/dart/frog/leg/emitter.dart
+++ b/dart/frog/leg/emitter.dart
@@ -107,7 +107,7 @@ function(child, parent) {
 
     int count = 0;
     parameters.forEachParameter((Element element) {
-      String jsName = JsNames.getValid('${element.name}');
+      String jsName = JsNames.getValid(element.name.slowToString());
       if (count < positionalArgumentCount) {
         parametersBuffer[count] = jsName;
         argumentsBuffer[count] = jsName;
@@ -234,7 +234,7 @@ function(child, parent) {
     }
 
     String className = namer.isolatePropertyAccess(classElement);
-    buffer.add('$className = function ${classElement.name}(');
+    buffer.add('$className = function ${classElement.name.slowToString()}(');
     StringBuffer bodyBuffer = new StringBuffer();
     // If the class is never instantiated we still need to set it up for
     // inheritance purposes, but we can leave its JavaScript constructor empty.
@@ -579,19 +579,21 @@ $prototype.toString = function() {
         for (Selector selector in selectors) {
           String jsName =
               namer.instanceMethodInvocationName(methodName, selector);
-          generateMethod(methodName.stringValue, jsName, selector);
+          generateMethod(methodName.slowToString(), jsName, selector);
         }
       }
     });
 
     compiler.universe.invokedGetters.forEach((SourceString getterName) {
       String jsName = namer.getterName(getterName);
-      generateMethod('get $getterName', jsName, Selector.GETTER);
+      generateMethod('get ${getterName.slowToString()}', jsName,
+                     Selector.GETTER);
     });
 
     compiler.universe.invokedSetters.forEach((SourceString setterName) {
       String jsName = namer.setterName(setterName);
-      generateMethod('set $setterName', jsName, Selector.SETTER);
+      generateMethod('set ${setterName.slowToString()}', jsName,
+                     Selector.SETTER);
     });
   }