function addToWorkingSet(file) {
        // If doc is already in working set, don't add it again
        if (findInWorkingSet(file.fullPath) !== -1) {
            return;
        }
        
        // Add
        _workingSet.push(file);
        
        // Add to MRU order: either first or last, depending on whether it's already the current doc or not
        if (_currentDocument && _currentDocument.file.fullPath === file.fullPath) {
            _workingSetMRUOrder.unshift(file);
        } else {
            _workingSetMRUOrder.push(file);
        }
        
        // Dispatch event
        $(exports).triggerHandler("workingSetAdd", file);
    }
Adds the given file to the end of the working set list, if it is not already in the list.
Does not change which document is currently open in the editor. Completes synchronously.
@param {!FileEntry} file