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

src/js/generator.js

Index: src/js/generator.js
diff --git a/src/js/generator.js b/src/js/generator.js
index 6240f7ad3f0aa288f4e9f3fcf73a670a3e32df2f..d4262dcc88c6c48e264b5cbfdf976f10897c01b5 100644
--- a/src/js/generator.js
+++ b/src/js/generator.js
@@ -84,9 +84,10 @@ function GeneratorFunctionConstructor(arg1) {  // length == 1
   var global_proxy = %GlobalProxy(GeneratorFunctionConstructor);
   // 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, GeneratorFunction, new.target);
 }
 
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