src/utils/repo.js
function fetchTree(repoState, driver, branch) {
    // Fetch a working tree for this branch
    return WorkingUtils.fetch(driver, branch)
    .then((newWorkingState) => {
        return updateWorkingState(repoState, branch, newWorkingState);
    });
}
function fetchTree(repoState, driver, branch) {
    // Fetch a working tree for this branch
    return WorkingUtils.fetch(driver, branch)
    .then((newWorkingState) => {
        return updateWorkingState(repoState, branch, newWorkingState);
    });
}
Fetches the given branch's tree, from its SHA, and __resets any
WorkingState for it__
@param {RepositoryState}
@param {Driver}
@param {Branch}
@return {Promise<RepositoryState>}