function markAsBeingEdited(controller)
        {
            this._editing = /** @type {!WebInspector.InplaceEditor.Controller} */ (controller);
            this._editing.setWidth(this.treeOutline.visibleWidth());
            this.treeOutline.setMultilineEditing(this._editing);
        }
@param {!Object} controller
@this {WebInspector.ElementsTreeElement}