Fast path for strict closure creation.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index ca78236aa2157eef69c4b9838d6272fd22ee2b4e..96ef755a1d745baa84badd5ac7547c55b536aabf 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -68,11 +68,15 @@ void FastNewClosureStub::Generate(MacroAssembler* masm) {
   // Get the function info from the stack.
   __ movq(rdx, Operand(rsp, 1 * kPointerSize));
 
+  int map_index = strict_mode_ == kStrictMode
+      ? Context::FUNCTION_MAP_STRICT_INDEX
+      : Context::FUNCTION_MAP_INDEX;
+
   // Compute the function map in the current global context and set that
   // as the map of the allocated object.
   __ movq(rcx, Operand(rsi, Context::SlotOffset(Context::GLOBAL_INDEX)));
   __ movq(rcx, FieldOperand(rcx, GlobalObject::kGlobalContextOffset));
-  __ movq(rcx, Operand(rcx, Context::SlotOffset(Context::FUNCTION_MAP_INDEX)));
+  __ movq(rcx, Operand(rcx, Context::SlotOffset(map_index)));
   __ movq(FieldOperand(rax, JSObject::kMapOffset), rcx);
 
   // Initialize the rest of the function. We don't have to update the