anchor.diff:  /// Concrete test runner of bytecode.
   class TestRunnerKBC implements TestRunner {
     TestRunnerKBC(String prefix, String tag, String top, String tmp, this.env,
  -      this.fileName, List<String> extraFlags) {
  +      this.fileName, List<String> extraFlags, bool kbcSrc) {
       description = '$prefix-$tag';
  -    generate = '$top/pkg/vm/tool/gen_kernel';
  -    platform = '--platform=$top/out/$tag/vm_platform_strong.dill';
  -    dill = '$tmp/out.dill';
       dart = '$top/out/$tag/dart';
  -    cmd = [dart] + extraFlags + [dill];
  +    if (kbcSrc) {
  +      cmd = [dart] + extraFlags + [fileName];
  +    } else {
  +      generate = '$top/pkg/vm/tool/gen_kernel';
  +      platform = '--platform=$top/out/$tag/vm_platform_strong.dill';
  +      dill = '$tmp/out.dill';
  +      cmd = [dart] + extraFlags + [dill];
  +    }
     }
   
     TestResult run() {
  -    TestResult result = runCommand(
  -        [generate, '--gen-bytecode', platform, '-o', dill, fileName], env);
  -    if (result.exitCode != 0) {
  -      return result;
  +    if (generate != null) {
  +      TestResult result = runCommand(
  +          [generate, '--gen-bytecode', platform, '-o', dill, fileName], env);
  +      if (result.exitCode != 0) {
  +        return result;
  +      }
       }
       return runCommand(cmd, env);
     }
  
positive.code:           prefix, tag, top, tmp, env, fileName, extraFlags);
      } else if (mode.startsWith('kbc')) {
        return new TestRunnerKBC(
            prefix, tag, top, tmp, env, fileName, extraFlags);
      } else if (mode.startsWith('djs')) {
        return new TestRunnerDJS(prefix, tag, top, tmp, env, fileName);
      }
  
negative.code:     } else if (mode.startsWith('kbc-cmp')) {
        prefix += '-CMP';
        extraFlags += ['--use-bytecode-compiler'];
      }
      // Every once in a while, go directly from source for kbc-*-x64.
      bool kbcSrc = false;
      if (mode.startsWith('kbc') &&
          mode.endsWith('x64') &&
          rand.nextInt(4) == 0) {
        prefix += '-SRC';
        kbcSrc = true;
      }
      // Every once in a while, stress test JIT.
      if (mode.startsWith('jit') && rand.nextInt(4) == 0) {
  