Classes: Add support for toString

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 782b953ea9763edf0dadbc32511d32a6deef0463..5adbca25b3b77b58379725f7b004cc161b7ed74a 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -1739,6 +1739,11 @@ function FunctionSourceString(func) {
     throw new $TypeError('Function.prototype.toString is not generic');
   }
 
+  var classSource = %ClassGetSourceCode(func);
+  if (IS_STRING(classSource)) {
+    return classSource;
+  }
+
   var source = %FunctionGetSourceCode(func);
   if (!IS_STRING(source) || %FunctionIsBuiltin(func)) {
     var name = %FunctionGetName(func);