anchor.diff:  import 'package:analyzer/dart/analysis/features.dart';
   import 'package:analyzer/error/listener.dart';
   import 'package:analyzer/file_system/file_system.dart';
  +import 'package:analyzer/file_system/overlay_file_system.dart';
   import 'package:analyzer/instrumentation/instrumentation.dart';
   import 'package:analyzer/src/dart/analysis/analysis_context_collection.dart';
   import 'package:analyzer/src/dart/analysis/byte_store.dart';
  
positive.code: /// Class that maintains a mapping from included/excluded paths to a set of
  /// folders that should correspond to analysis contexts.
  class ContextManagerImpl implements ContextManager {
    /// The [ResourceProvider] using which paths are converted into [Resource]s.
    final ResourceProvider resourceProvider;
  
    /// The manager used to access the SDK that should be associated with a
    /// particular context.
  
negative.code:     }
  
      var collection = _collection;
      if (collection != null &&
          file_paths.isDart(pathContext, path) &&
          // If this resource has an overlay, then the change on disk will never
          // affect analysis results so can be skipped. Removing the overlay will
          // re-read the contents from disk.
          !resourceProvider.hasOverlay(path)) {
        for (var analysisContext in collection.contexts) {
          switch (type) {
            case ChangeType.ADD:
  