Fix a bug in delete for lookup slots.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 896e53da60425c5641f12977e69f3cc9ed1a7d92..da1a7aee44b0600b12f38c8d6a92a92caadf9fb4 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -3006,19 +3006,18 @@ void FullCodeGenerator::VisitUnaryOperation(UnaryOperation* expr) {
         if (prop != NULL) {
           VisitForStackValue(prop->obj());
           VisitForStackValue(prop->key());
+          __ InvokeBuiltin(Builtins::DELETE, CALL_FUNCTION);
         } else if (var->is_global()) {
           __ push(GlobalObjectOperand());
           __ Push(var->name());
+          __ InvokeBuiltin(Builtins::DELETE, CALL_FUNCTION);
         } else {
-          // Non-global variable.  Call the runtime to look up the context
-          // where the variable was introduced.
+          // Non-global variable.  Call the runtime to delete from the
+          // context where the variable was introduced.
           __ push(context_register());
           __ Push(var->name());
-          __ CallRuntime(Runtime::kLookupContext, 2);
-          __ push(rax);
-          __ Push(var->name());
+          __ CallRuntime(Runtime::kDeleteContextSlot, 2);
         }
-        __ InvokeBuiltin(Builtins::DELETE, CALL_FUNCTION);
         context()->Plug(rax);
       }
       break;