fix: fix member of ScriptWrappable not tracked by GC.

[andycall]

The basic rule when using in ScriptWrappable is that it must be tracked by GCVisitor.

This patch fixes a bug in touch_list.cc caused by the Trace() function bypassing the aforementioned rules.

void TouchList::Trace(GCVisitor* visitor) const {
  for (auto& item : values_) {
    item->Trace(visitor); // This line of code bypass the tracing of GC.
  }
}