anchor.diff:    List<int> exitCodes =
         await Future.wait(startedProcesses.map((e) => e.process.exitCode));
     if (exitCodes.where((e) => e != 0).isNotEmpty) {
  +    print("\n\nFound failures!:\n");
       // At least one failed.
  -    exitCode = 1;
       for (WrappedProcess p in startedProcesses) {
         int pExitCode = await p.process.exitCode;
         if (pExitCode != 0) {
           print("${p.id} failed with exist-code $pExitCode");
         }
       }
  +
  +    throw "There were failures!";
     }
   }
  -
  -List<String> observatoryLines = [];
   
   Future<WrappedProcess> run(List<String> args, String id) async {
     Stopwatch stopwatch = new Stopwatch()..start();
     Process process = await Process.start(
         Platform.resolvedExecutable, ["--enable-asserts", ...args]);
  +  List<String> observatoryLines = [];
     process.stderr
         .transform(utf8.decoder)
         .transform(new LineSplitter())
  
positive.code:       "\n\n");
  
    List<WrappedProcess> startedProcesses = [];
    {
      // Very slow: Leak-test.
      Uri leakTester =
  
negative.code:     } else {
        // The tools/bots/flutter/compile_flutter.sh script passes `--path`
        // --- we'll just pass everything along.
        leakTest = await run(
          [
            leakTester.toString(),
            ...args,
          ],
          "leak test",
        );
        startedProcesses.add(leakTest);
      }
    }
    {
  