code: function()
      {
          if (this._savedChildren)
              return;
  
          this._savedSelfTime = this.selfTime;
          this._savedTotalTime = this.totalTime;
          this._savedNumberOfCalls = this.numberOfCalls;
  
          this._savedChildren = this.children.slice();
      }
docs: When focusing and collapsing we modify lots of nodes in the tree. This allows us to restore them all to their original state when we revert.