anchor.diff:  
     @override
     Source mapDartUri(String dartUri) {
  +    Source source = _uriToSourceMap[dartUri];
  +    if (source == null) {
  +      source = _mapDartUri(dartUri);
  +      _uriToSourceMap[dartUri] = source;
  +    }
  +    return source;
  +  }
  +
  +  /**
  +   * Return the [SdkBundle] for this SDK, if it exists, or `null` otherwise.
  +   */
  +  SdkBundle _getSummarySdkBundle() {
  +    String rootPath = directory.getAbsolutePath();
  +    String path = pathos.join(rootPath, 'lib', '_internal', 'analysis_summary');
  +    try {
  +      File file = new File(path);
  +      if (file.existsSync()) {
  +        List<int> bytes = file.readAsBytesSync();
  +        return new SdkBundle.fromBuffer(bytes);
  +      }
  +    } catch (exception, stackTrace) {
  +      AnalysisEngine.instance.logger.logError(
  +          'Failed to load SDK analysis summary from $path',
  +          new CaughtException(exception, stackTrace));
  +    }
  +    return null;
  +  }
  +
  +  FileBasedSource _mapDartUri(String dartUri) {
       String libraryName;
       String relativePath;
       int index = dartUri.indexOf('/');
  
positive.code:     } on URISyntaxException {
        return null;
      }
    }
  
    /**
     * Return the [SdkBundle] for this SDK, if it exists, or `null` otherwise.
     */
    SdkBundle _getSummarySdkBundle() {
      String rootPath = directory.getAbsolutePath();
      String path = pathos.join(rootPath, 'lib', '_internal', 'analysis_summary');
      try {
        File file = new File(path);
        if (file.existsSync()) {
          List<int> bytes = file.readAsBytesSync();
          return new SdkBundle.fromBuffer(bytes);
        }
      } catch (exception, stackTrace) {
        AnalysisEngine.instance.logger.logError(
            'Failed to load SDK analysis summary from $path',
            new CaughtException(exception, stackTrace));
      }
      return null;
    }
  
    /**
  
negative.code: 
  library analyzer.src.generated.sdk_io;
  
  import 'dart:collection';
  import 'dart:io';
  
  import 'package:analyzer/src/context/context.dart';
  