message: Fix unused private field warning.
diff: @@ -195,7 +195,10 @@ private:
  UniformInterfaceBlock mUniformInterfaceBlock;
  SubpassInfo mSubpassInfo;
  SamplerBindingMap mSamplerBindings;
  +
  +#if FILAMENT_ENABLE_MATDBG
  matdbg::MaterialKey mDebuggerId;
  +#endif
  utils::CString mName;
  FEngine& mEngine;
  