disable backbuffer preservation when possible, which may improve performance a bit

    surface = eglCreateWindowSurface(display, config, mNativeWindow.get(), NULL);

    if (mFlags & UPDATE_ON_DEMAND) {

        // if we have update on demand, we definitely don't need to

        // preserve the backbuffer, which is usually costly.

        eglSurfaceAttrib(display, surface,

                EGL_SWAP_BEHAVIOR, EGL_BUFFER_DESTROYED);

    }

    if (eglQuerySurface(display, surface, EGL_SWAP_BEHAVIOR, &dummy) == EGL_TRUE) {

        if (dummy == EGL_BUFFER_PRESERVED) {

            mFlags |= BUFFER_PRESERVED;