function handleFileAddToWorkingSet(commandData) {
        return handleFileOpen(commandData).done(function (doc) {
            // addToWorkingSet is synchronous
            DocumentManager.addToWorkingSet(doc.file);
        });
    }
Opens the given file, makes it the current document, AND adds it to the working set.
@param {!{fullPath:string}} Params for FILE_OPEN command