Revert "Void is not required to be `null` anymore."

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 42529f413b4f9277395cf1d794fa8d0f9d48d700..b84ff432b148e51d09357732980b877ecbf615ea 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -3415,6 +3415,11 @@ listSuperNativeTypeCast(value, property) {
   propertyTypeCastError(value, property);
 }
 
+voidTypeCheck(value) {
+  if (value == null) return value;
+  throw new TypeErrorImplementation(value, 'void');
+}
+
 extractFunctionTypeObjectFrom(o) {
   var interceptor = getInterceptor(o);
   var signatureName = JS_GET_NAME(JsGetName.SIGNATURE_NAME);