function showInTree(entry) {
        return model.showInTree(entry).then(_saveTreeState);
    }
Expands tree nodes to show the given file or folder and selects it. Silently no-ops if the
path lies outside the project, or if it doesn't exist.

@param {!(File|Directory)} entry File or Directory to show
@return {$.Promise} Resolved when done; or rejected if not found