Fix Mac64-debug issue introduced with r21154.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/271443002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21155 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-codegen-x64.cc

@@ -1692,6 +1692,7 @@ void LCodeGen::DoConstantE(LConstantE* instr) {
 
 void LCodeGen::DoConstantT(LConstantT* instr) {
   Handle<Object> object = instr->value(isolate());
+  AllowDeferredHandleDereference smi_check;
   if (instr->hydrogen()->HasObjectMap()) {
     Handle<Map> object_map = instr->hydrogen()->ObjectMap().handle();
     CHECK(object->IsHeapObject());