anchor.diff:     * A cache of content used to override the default content of a source.
      */
     ContentCache _contentCache = new ContentCache();
  -
  -  /**
  -   * A cache of content used to override the default content of a source
  -   * before the corresponding override was removed from [_contentCache].
  -   */
  -  LRUMap<Source, String> _prevOverlayCache = new LRUMap<Source, String>(5);
   
     /**
      * The source factory used to create the sources that can be analyzed in this context.
  
positive.code:       return;
      }
      // Check if the content of the source is the same as it was the last time.
      String sourceContent = _prevOverlayCache.get(source);
      if (sourceContent != null) {
        try {
          TimestampedData<String> fileContents = getContents(source);
          if (fileContents.data == sourceContent) {
  
negative.code: import 'package:analyzer/src/generated/incremental_resolution_validator.dart';
  import 'package:analyzer/src/services/lint.dart';
  import 'package:analyzer/src/task/task_dart.dart';
  
  import '../../instrumentation/instrumentation.dart';
  import 'ast.dart';
  