anchor.diff:  
   import '../src/common.dart';
   
  -const String _kInitialVersion = 'v1.9.1+hotfix.6';
  -const String _kBranch = 'stable';
  +const String _kInitialVersion = 'v1.9.1';
  +const String _kBranch = 'dev';
   const FileSystem fileSystem = LocalFileSystem();
   const ProcessManager processManager = LocalProcessManager();
   final Stdio stdio = Stdio();
  
positive.code:     final Directory testDirectory = parentDirectory.childDirectory('flutter');
      testDirectory.createSync(recursive: true);
  
      // Enable longpaths for windows integration test.
      await processManager.run(<String>[
        'git', 'config', '--system', 'core.longpaths', 'true',
      ]);
  
      // Step 1. Clone the dev branch of flutter into the test directory.
      await processUtils.stream(<String>[
        'git',
        'clone',
        'https://github.com/flutter/flutter.git',
      ], workingDirectory: parentDirectory.path, trace: true);
  
      // Step 2. Switch to the dev branch.
      await processUtils.stream(<String>[
        'git',
        'checkout',
        '--track',
  
negative.code:     expect(versionResult.stdout, isNot(contains(_kInitialVersion)));
  
      // Step 6. Downgrade back to initial version.
      exitCode = await processUtils.stream(<String>[
         flutterBin,
        'downgrade',
        '--no-prompt',
        '--working-directory=${testDirectory.path}'
      ], workingDirectory: testDirectory.path, trace: true);
      expect(exitCode, 0);
  
      // Step 7. Verify downgraded version matches original version.
      final RunResult oldVersionResult = await processUtils.run(<String>[
  