How do Windows Store apps built from Unity support changing the window size?

void Start()
{
# if UNITY_METRO
    UnityEngine.WSA.Application.windowSizeChanged+=Application_windowSizeChanged;
#endif
}

void Application_windowSizeChanged(int width, int height)
{
    // set the desired aspect ratio (the values in this example are)
    // hard-coded for 16:9, but you could make them into public
    // variables installed so you can set them at design time)
    float targetaspect = 16.0f/9.0f;

    // determine the game window's current aspect ratio
    float windowaspect=(float)width/(float)height;

    // current viewport height should be scaled by this amount
    float scaleheight=windowaspect/targetaspect;

    // obtain camera component so we can modify its viewport
    Camera camera=GameObject.Find("mainCamera").camera;
    if(camera==null)
    {
        return;
    }

    // if scaled height is less than current height, add letterbox
    if(scaleheight<1.0f)
    {
        Correct = camera.rect;

        rect.width = 1.0f;
        rect.height = scaleheight;
        rect.x = 0;
        rect.y = (1.0f-scaleheight)/2.0f;

        camera.rect=rect;
    }
    else//add pillarbox
    {
        float scalewidth = 1.0f/scaleheight;

        Correct = camera.rect;

        rect.width = scalewidth;
        rect.height=1.0f;
        rect.x = (1.0f-scalewidth)/2.0f;
        rect.y = 0;

        camera.rect=rect;
    }

}