code: function layerContainsFontFace (layer, fontFace) {
    // Check the layer itself.
    if (layer.type === 'text' && layer.fontFace && layer.fontFace.id === fontFace.id) {
      return layer;
    }
  
    // Check the layer's children.
    if (layer.children) {
      for (var i=0, len=layer.children.length; i < len; i++) {
        if (layerContainsFontFace(layer.children[i], fontFace)) {
          return layer.children[i];
        }
      }
    }
  
    return false;
  }
docs: Check if a layer is using a given FontFace.
  
  @param {RenderLayer} layer
  @param {FontFace} fontFace
  @return {Boolean}