CDS dumping code calls TRAPS functions in VM thread

void DynamicArchiveBuilder::sort_methods(InstanceKlass* ik) const {
  ...
  Thread* THREAD = Thread::current();
  ...
  ik->vtable().initialize_vtable(true, THREAD); assert(!HAS_PENDING_EXCEPTION, "cannot fail");
  ik->itable().initialize_itable(true, THREAD); assert(!HAS_PENDING_EXCEPTION, "cannot fail");
}

The code works today because the two calls should never throw exceptions (there are no allocations, no loader constraint check, etc).

However, if we change TRAPS to be JavaThread*, we will not be able to do this anymore. (See JDK-8252685).