gistfile1.js

  topToolbarDidChange: function() {
    var active = this.activeTopToolbar, replacement = this.get("topToolbar");
    
    // if we have an active toolbar, set the build direction and build out
    if (active) {
      if (this._currentDirection !== null) {
        active.set("buildDirection", this._currentDirection);
        this.buildOutChild(active);
      } else {
        this.removeChild(active);
      }
    }
    
    // if we have a new toolbar, set the build direction and build in
    if (replacement) {
      if (this._currentDirection !== null) {
        replacement.set("buildDirection", this._currentDirection);
        this.buildInChild(replacement);
      } else {
        this.appendChild(replacement);
      }
    }
    
    // update, and queue retiling
    this.activeTopToolbar = replacement;
    this.invokeOnce("childDidChange");
  }.observes("topToolbar"),