message: only fire onCollapsed once when changing
diff: @@ -26,25 +26,29 @@ class CollapseDistributor extends FixedDistributor {
  super(sizer, item, config);
  this.toggleSize = config && config.toggleSize;
  this.onCollapsed = config && config.onCollapsed;
  + this.isCollapsed = false;
  }
  resize(offset) {
  let newSize = this.sizeFromOffset(offset);
  - if (newSize < this.toggleSize) {
  - this.item.classList.add("collapsed");
  + const isCollapsedSize = newSize < this.toggleSize;
  + if (isCollapsedSize && !this.isCollapsed) {
  + this.isCollapsed = true;
  if (this.onCollapsed) {
  this.onCollapsed(true, this.item);
  }
  }
  - else {
  - this.item.classList.remove("collapsed");
  + else if (!isCollapsedSize && this.isCollapsed) {
  if (this.onCollapsed) {
  this.onCollapsed(false, this.item);
  }
  + this.isCollapsed = false;
  }
  + if (!isCollapsedSize) {
  super.resize(offset);
  }
  }
  +}
  class PercentageDistributor {
  