anchor.diff:    ///
     /// Otherwise the driver will compute new kernel files and return them.
     Future<KernelResult> getKernel(Uri uri) async {
  -    return await _logger.runAsync('Compute delta', () async {
  +    return await runWithFrontEndContext('Compute delta', () async {
         await _refreshInvalidatedFiles();
   
         // Ensure that the graph starting at the entry point is ready.
  
positive.code:       });
  
        return new KernelResult(nameRoot, results);
      });
    }
  
  
negative.code: 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';
  