DisplayDevice doesn't need weak pointers or polymorphism

class LayerBase;

class SurfaceFlinger;

class DisplayDevice : public virtual RefBase

class DisplayDevice : public LightRefBase<DisplayDevice>

{

public:

    // region in layer-stack space

            const sp<ANativeWindow>& surface,

            EGLConfig config);

    virtual ~DisplayDevice();

    ~DisplayDevice();

    // whether this is a valid object. An invalid DisplayDevice is returned

    // when an non existing id is requested