anchor.diff:     */
     Future<String> _revisionAt(PackageId id) {
       return runProcess("git", ["rev-parse", _getEffectiveRef(id)],
  -        workingDir: _repoCachePath(id), pipeStderr: true).transform((result) {
  +        workingDir: _repoCachePath(id)).transform((result) {
         if (!result.success) throw 'Git failed.';
         return result.stdout[0];
       });
  
positive.code:    * Checks out the reference [ref] in [repoPath].
     */
    Future _checkOut(String repoPath, String ref) {
      return runProcess("git", ["checkout", ref], pipeStdout: true,
          pipeStderr: true, workingDir: repoPath).transform((result) {
        if (!result.success) throw 'Git failed.';
        return null;
      });
  
negative.code:    * Clones the repo at the URI [from] to the path [to] on the local filesystem.
     */
    Future _clone(String from, String to) {
      return runProcess("git", ["clone", from, to]).transform((result) {
        if (!result.success) throw 'Git failed.';
        return null;
      });
  