anchor.diff:      }
     }
   
  +  String customScheme = "org-dartlang-sdk";
  +  var fileSystem = MultiRootFileSystem(
  +      customScheme, [Uri.base], StandardFileSystem.instance);
  +  Uri sdkRoot = Uri.parse("$customScheme:/");
  +  Uri packagesFileUri = sdkRoot
  +      .resolve(p.relative(Uri.file(packagesPath).path, from: Uri.base.path));
  +  if (packagesFileUri.scheme != customScheme) {
  +    throw "packagesPath has to be under ${Uri.base}";
  +  }
  +  Uri librariesSpecificationUri = sdkRoot
  +      .resolve(p.relative(Uri.file(librarySpecPath).path, from: Uri.base.path));
  +  if (librariesSpecificationUri.scheme != customScheme) {
  +    throw "librarySpecPath has to be under ${Uri.base}";
  +  }
  +
     var options = CompilerOptions()
       ..compileSdk = true
  -    // TODO(sigmund): remove these two unnecessary options when possible.
  -    ..sdkRoot = Uri.base
  -    ..packagesFileUri = Uri.base.resolveUri(Uri.file(packagesPath))
  -    ..librariesSpecificationUri = Uri.base.resolveUri(Uri.file(librarySpecPath))
  +    ..fileSystem = fileSystem
  +    ..sdkRoot = sdkRoot
  +    ..packagesFileUri = packagesFileUri
  +    ..librariesSpecificationUri = librariesSpecificationUri
       ..target = target
       ..onDiagnostic = onDiagnostic
       ..environmentDefines = {};
   
     var inputs = target.extraRequiredLibraries.map(Uri.parse).toList();
  +
     var compilerResult = await kernelForModule(inputs, options);
     var component = compilerResult.component;
   
  
positive.code:     var mapPath = '$jsPath.map';
      await Directory(jsDir).create();
      var jsCode = jsProgramToCode(jsModule, format,
          jsUrl: jsPath, mapUrl: mapPath, buildSourceMap: true);
      await File(jsPath).writeAsString(jsCode.code);
      await File(mapPath).writeAsString(json.encode(jsCode.sourceMap));
    }
  
negative.code: import 'dart:convert' show json;
  import 'dart:io';
  import 'package:args/args.dart' show ArgParser;
  import 'package:build_integration/file_system/multi_root.dart';
  import 'package:dev_compiler/src/compiler/module_builder.dart';
  import 'package:dev_compiler/src/compiler/shared_command.dart'
      show SharedCompilerOptions;
  