anchor.diff:  import 'package:front_end/file_system.dart';
   import 'package:front_end/src/base/api_signature.dart';
   import 'package:front_end/src/base/performace_logger.dart';
  +import 'package:front_end/src/fasta/compiler_command_line.dart';
  +import 'package:front_end/src/fasta/compiler_context.dart';
   import 'package:front_end/src/fasta/dill/dill_library_builder.dart';
   import 'package:front_end/src/fasta/dill/dill_target.dart';
   import 'package:front_end/src/fasta/kernel/kernel_target.dart';
  
positive.code:   ///
    /// Otherwise the driver will compute new kernel files and return them.
    Future<KernelResult> getKernel(Uri uri) async {
      return await _logger.runAsync('Compute delta', () async {
        await _refreshInvalidatedFiles();
  
        // Ensure that the graph starting at the entry point is ready.
  
negative.code:       });
  
        return new KernelResult(nameRoot, results);
      });
    }
  
    Future<T> runWithFrontEndContext<T>(String msg, Future<T> f()) async {
      return await CompilerCommandLine.withGlobalOptions("", [""],
          (CompilerContext context) {
        context.options.options["--target"] = _target;
        context.options.options["report"] = (message, severity) {};
        context.options.options["reportWithoutLocation"] = (message, severity) {};
        return _logger.runAsync(msg, f);
      });
    }
  
  