anchor.diff:          byteDelete = true;
         } else if (arg == "--ask-redirect-target") {
           askAboutRedirectCrashTarget = true;
  +      } else if (arg.startsWith("--stack-matches=")) {
  +        String stackMatches = arg.substring("--stack-matches=".length);
  +        stackTraceMatches = int.parse(stackMatches);
         } else {
           throw "Unknown option $arg";
         }
  
positive.code: String expectedCrashLine;
  bool byteDelete = false;
  bool askAboutRedirectCrashTarget = false;
  Set<String> askedAboutRedirect = {};
  
  main(List<String> arguments) async {
  
negative.code:     // Find line with #0 in it.
      String eWithSt = "$e\n\n$st";
      List<String> lines = eWithSt.split("\n");
      String foundLine = "";
      int lookFor = 0;
      for (String line in lines) {
        if (line.startsWith("#$lookFor")) {
          foundLine += line;
          lookFor++;
          if (lookFor >= stackTraceMatches) {
            break;
          } else {
            foundLine += "\n";
          }
        }
      }
      if (foundLine == null) throw "Unexpected crash without stacktrace: $e";
      if (expectedCrashLine == null) {
        print("Got '$foundLine'");
        expectedCrashLine = foundLine;
        return true;
      } else if (foundLine == expectedCrashLine) {
  