anchor.diff:  
   import 'dart:io' show File;
   
  -import 'package:analyzer/src/generated/sdk.dart' show DartSdk;
  -
  -import 'package:analyzer/src/kernel/loader.dart' show DartLoader;
  -
   import 'package:testing/testing.dart'
  -    show Chain, Result, Step, TestDescription, runMe;
  +    show Chain, ChainContext, Result, Step, TestDescription, runMe;
   
   import 'package:kernel/ast.dart' show Program, Library;
   
  -import 'package:kernel/target/targets.dart' show Target, TargetFlags, getTarget;
  -
  -import 'package:front_end/src/fasta/testing/kernel_chain.dart';
  +import 'package:front_end/src/fasta/testing/kernel_chain.dart' show runDiff;
   
   import 'package:front_end/src/fasta/ticker.dart' show Ticker;
   
  
positive.code:     } on InputError catch (e, s) {
        return fail(null, e.error, s);
      }
  
      return pass(p);
    }
  }
  
negative.code: 
    Future<Result<Program>> run(
        TestDescription description, InterpreterContext context) async {
      Program platform = await context.loadPlatform();
      Ticker ticker = new Ticker();
      DillTarget dillTarget = new DillTarget(ticker, context.uriTranslator);
      dillTarget.loader
        ..input = Uri.parse("org.dartlang:platform") // Make up a name.
        ..setProgram(platform);
      KernelTarget sourceTarget =
          new KernelTarget(dillTarget, context.uriTranslator, context.strongMode);
  
      Program p;
      try {
  