anchor.diff:  typedef void CompilerMessageConsumer(String message);
   
   class CompilerOutput {
  -  String outputFilename;
  -  int errorCount;
  -
  -  CompilerOutput(this.outputFilename, this.errorCount);
  +  final String outputFilename;
  +  final int errorCount;
  +
  +  const CompilerOutput(this.outputFilename, this.errorCount);
   }
   
   class _StdoutHandler {
  
positive.code:     String incrementalCompilerByteStorePath,
      String packagesPath,
      List<String> fileSystemRoots,
      String fileSystemScheme}) async {
      final String frontendServer = artifacts.getArtifactPath(
        Artifact.frontendServerSnapshotForEngineDartSdk
      );
  
negative.code: class KernelCompiler {
    const KernelCompiler();
  
    Future<CompilerOutput> compile({
      String sdkRoot,
      String mainPath,
      String outputFilePath,
      String depFilePath,
  