WebRender does blurring via multiple passes, first it scales the source down using scale tasks and then does a horizontal and vertical blur pass. To ensure that errors are not introduced due to scaling, the width and height of the source must be multiples of two.
When blurring for backdrop-filter, we do not adjust the size so it is a multiple of two because this can add extra padding of transparent pixels to the source. This results in incorrect blur results.
We should do size adjustment but also track the original size so we don't include the extra transparent padding while computing the blur.