Function local_content_layer_for 

pub fn local_content_layer_for(layer: &GraphicsLayer) -> GraphicsLayer

local_content_layer(&layer_for_content(layer, isolation)) without building either intermediate. The content layer differs from layer only in the alpha the isolation moves to the composite step, and the local layer keeps just that alpha and the colour filter, so the two clones the composed form performs — one GraphicsLayer, one RenderEffect — are pure waste.