[Isolates] Merge 7051:7083 from bleeding_edge to isolates.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
===================================================================
--- src/x64/full-codegen-x64.cc	(revision 7083)
+++ src/x64/full-codegen-x64.cc	(working copy)
@@ -200,11 +200,14 @@
     // stack frame was an arguments adapter frame.
     ArgumentsAccessStub stub(ArgumentsAccessStub::NEW_OBJECT);
     __ CallStub(&stub);
-    // Store new arguments object in both "arguments" and ".arguments" slots.
-    __ movq(rcx, rax);
+
+    Variable* arguments_shadow = scope()->arguments_shadow();
+    if (arguments_shadow != NULL) {
+      // Store new arguments object in both "arguments" and ".arguments" slots.
+      __ movq(rcx, rax);
+      Move(arguments_shadow->AsSlot(), rcx, rbx, rdx);
+    }
     Move(arguments->AsSlot(), rax, rbx, rdx);
-    Slot* dot_arguments_slot = scope()->arguments_shadow()->AsSlot();
-    Move(dot_arguments_slot, rcx, rbx, rdx);
   }
 
   if (FLAG_trace) {