anchor.diff:  
   Logger _logger = new Logger('pub');
   
  +/**
  + * This class has two general functions:
  + *
  + * Given a list of packages, resolve the list to the full transitive set of
  + * referenced packages and their versions. This uses an implicit `any`
  + * constraint. It will resolve to the lastest non-dev versions that satisfy
  + * their mutual constraints.
  + *
  + * And, given a package and a version, it can return a local directory with the
  + * contents of the package's `lib/` folder. This will download the
  + * package+version from pub.dartlang.org and store it in a disk cache. As the
  + * cache is populated the cost of asking for a package's `lib/` folder contents
  + * will go to zero.
  + *
  + */
   class Pub {
     Directory _cacheDir;
   
  
positive.code:   String toString() => '${packages}';
  }
  
  class PackageInfo {
    final String name;
    final String version;
  
negative.code:   }
  }
  
  /**
   * A set of packages.
   */
  class PackagesInfo {
    final List<PackageInfo> packages;
  
  