fixes #616, statics on callable functions

tool/input_sdk/private/ddc_runtime/classes.dart

Index: tool/input_sdk/private/ddc_runtime/classes.dart
diff --git a/tool/input_sdk/private/ddc_runtime/classes.dart b/tool/input_sdk/private/ddc_runtime/classes.dart
index e34a3fa11f80765c17a0b52b4701f92aaf72e7bd..6bef0d699f3413ba4194c93dc0746f471b210e65 100644
--- a/tool/input_sdk/private/ddc_runtime/classes.dart
+++ b/tool/input_sdk/private/ddc_runtime/classes.dart
@@ -468,7 +468,7 @@ callableClass(callableCtor, classExpr) {
   // We're not going to use the original class, so we can safely replace it to
   // point at this constructor for the runtime type information.
   JS('', '#.prototype.constructor = #', callableCtor, callableCtor);
-  JS('', '#.__proto__ = #.__proto__', callableCtor, classExpr);
+  JS('', '#.__proto__ = #', callableCtor, classExpr);
   return callableCtor;
 }