anchor.diff:  import 'package:analyzer/src/generated/source.dart';
   import 'package:analyzer/src/generated/source_io.dart';
   import 'package:analyzer/src/summary/format.dart';
  +import 'package:analyzer/src/summary/idl.dart';
  +import 'package:analyzer/src/summary/prelink.dart';
   import 'package:analyzer/src/summary/summarize_ast.dart';
   import 'package:kernel/analyzer/loader.dart';
   import 'package:kernel/kernel.dart';
  
positive.code:           parseTimer.elapsedMicroseconds);
  }
  
  /// Add to [files] all sources reachable from [start].
  void collectSources(Source start, Set<Source> files) {
    if (!files.add(start)) return;
  
negative.code:       Set<Source> files = scanReachableFiles(entryUri);
        // TODO(sigmund): replace the warmup with instrumented snapshots.
        for (int i = 0; i < 10; i++) unlinkedSummarizeFiles(files);
      },
      'prelinked_summarize': () async {
        Set<Source> files = scanReachableFiles(entryUri);
        // TODO(sigmund): replace the warmup with instrumented snapshots.
        for (int i = 0; i < 10; i++) prelinkedSummarizeFiles(files);
      }
    };
  
  