[es6] Consistently use %_GetSuperConstructor to implement super calls.

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 4050991a387c1b628d48ea0708fc7e753b4d876c..21dd3e87b4e7ba19e44d7bf43b26963d63dc124b 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -2880,8 +2880,13 @@ void FullCodeGenerator::EmitSuperConstructorCall(Call* expr) {
       expr->expression()->AsSuperCallReference();
   DCHECK_NOT_NULL(super_call_ref);
 
-  EmitLoadSuperConstructor(super_call_ref);
-  __ Push(result_register());
+  // Push the super constructor target on the stack (may be null,
+  // but the Construct builtin can deal with that properly).
+  VisitForAccumulatorValue(super_call_ref->this_function_var());
+  __ AssertFunction(result_register());
+  __ movp(result_register(),
+          FieldOperand(result_register(), HeapObject::kMapOffset));
+  __ Push(FieldOperand(result_register(), Map::kPrototypeOffset));
 
   // Push the arguments ("left-to-right") on the stack.
   ZoneList<Expression*>* args = expr->arguments();