[es6] Fix Function and GeneratorFunction built-ins subclassing.

src/js/v8natives.js

Index: src/js/v8natives.js
diff --git a/src/js/v8natives.js b/src/js/v8natives.js
index 3c1e175a9e7f4f1bd8b23678b85c6722ea1d9f9a..dae087ded436e361b2610e8d99c634d6aace27a2 100644
--- a/src/js/v8natives.js
+++ b/src/js/v8natives.js
@@ -1797,9 +1797,10 @@ function FunctionConstructor(arg1) {  // length == 1
   var global_proxy = %GlobalProxy(FunctionConstructor);
   // Compile the string in the constructor and not a helper so that errors
   // appear to come from here.
-  var f = %_CallFunction(global_proxy, %CompileString(source, true));
-  %FunctionMarkNameShouldPrintAsAnonymous(f);
-  return f;
+  var func = %_CallFunction(global_proxy, %CompileString(source, true));
+  // Set name-should-print-as-anonymous flag on the SFI and ensure that

[Toon Verwaest, 2015/10/30 10:58:01]

 write out sfi

[Igor Sheludko, 2015/10/30 11:08:57]

Done.

+  // |func| uses correct initial map from |new.target| if it's available.
+  return %CompleteFunctionConstruction(func, GlobalFunction, new.target);
 }