src: use smart pointer in AsyncWrap::WeakCallback

PR-URL: nodejs#19168
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Author: danbev

src/async_wrap.cc

@@ -415,14 +415,14 @@ void AsyncWrap::WeakCallback(const v8::WeakCallbackInfo<DestroyParam>& info) {
   HandleScope scope(info.GetIsolate());
 
   Environment* env = Environment::GetCurrent(info.GetIsolate());
-  DestroyParam* p = info.GetParameter();
+  std::unique_ptr<DestroyParam> p{info.GetParameter()};
   Local<Object> prop_bag = PersistentToLocal(info.GetIsolate(), p->propBag);
 
   Local<Value> val = prop_bag->Get(env->destroyed_string());
   if (val->IsFalse()) {
     AsyncWrap::EmitDestroy(env, p->asyncId);
   }
-  delete p;
+  // unique_ptr goes out of scope here and pointer is deleted.
 }