anchor.diff:        env.sdkRoot =
           join(absolute(normalize(Platform.environment["SDK_ROOT"])), "lib");
       } else {
  -      throw "No SDK root found, please specify one using --sdk-root.";
  +      fail("No SDK root found, please specify one using --sdk-root.");
       }
     } else {
       env.sdkRoot = join(absolute(normalize(args["sdk-root"])), "lib");
     }
     if (!FileSystemEntity.isDirectorySync(env.sdkRoot)) {
  -    throw "Provided SDK root ${args["sdk-root"]} is not a valid SDK "
  -          "top-level directory";
  +    fail("Provided SDK root '${args["sdk-root"]}' is not a valid SDK "
  +         "top-level directory");
     }
   
     if (args["package-root"] == null) {
  
positive.code:   // off by at max (#workers - 1).
    var p = spawnFunction(worker);
    workerPorts.add(p);
    p.send(new Message(Message.WORK, [sharedEnv, files]), port);
  
    return 0;
  }
  
negative.code: 
  /// [Resolver] resolves imports with respect to a given environment.
  class Resolver {
    static const DART_PREFIX = "dart:";
    static const PACKAGE_PREFIX = "package:";
    static const FILE_PREFIX = "file://";
    static const HTTP_PREFIX = "http://";
  
    Map _env;
    List failed = [];
  