code: public final void setDebugger(Debugger debugger, Object contextData)
      {
          if (sealed) onSealedMutation();
          this.debugger = debugger;
          debuggerData = contextData;
      }
docs: Set the associated debugger.
  @param debugger the debugger to be used on callbacks from
  the engine.
  @param contextData arbitrary object that debugger can use to store
  per Context data.