anchor.diff:      return;
     }
   
  -  if (argResults.rest.length != 2) {
  +  var remainingArgs = []..addAll(argResults.rest);
  +
  +  if (remainingArgs.length == 1) {
  +    remainingArgs.add(remainingArgs.first);
  +  }
  +
  +  if (remainingArgs.length != 2) {
       usage(argParser);
       exit(1);
     }
  
positive.code: 
    var tests = scanTests();
  
    var startIndex = findFork(tests, argResults.rest[0]);
    var endIndex = findFork(tests, argResults.rest[1]);
  
    if (startIndex == null || endIndex == null) exit(1);
  
  
negative.code:   // dart2js-jsshell?
    "analyzer": [analyzer, noRuntime, useSdk],
    "analyzer-checked": [analyzer, noRuntime, checked, useSdk],
    "analyzer-checked-strong": [analyzer, noRuntime, checked, strong, useSdk],
    "analyzer-strong": [analyzer, noRuntime, strong, useSdk],
    "dart2js": [dart2js, chrome, useSdk, dart2jsBatch],
    "dart2js-d8-checked": [dart2js, d8, checked, fastStartup, useSdk, dart2jsBatch],
    "dart2js-jsshell": [dart2js, jsshell, fastStartup, useSdk, dart2jsBatch],
    // TODO(rnystrom): Is it worth running dart2js on Firefox too?
    "dartdevc": [dartdevc, chrome, useSdk, strong],
  