anchor.diff:  import 'package:analysis_server/src/services/refactoring/refactoring_internal.dart';
   import 'package:analyzer/dart/analysis/results.dart';
   import 'package:analyzer/dart/ast/ast.dart';
  +import 'package:analyzer/dart/element/element.dart';
   import 'package:analyzer/file_system/file_system.dart';
   import 'package:analyzer/src/dart/analysis/driver.dart';
  +import 'package:analyzer/src/dart/element/element.dart';
   import 'package:analyzer/src/generated/source.dart';
   import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
   import 'package:analyzer_plugin/utilities/range_factory.dart';
  
positive.code:     }
    }
  }
  
negative.code:   }
  
    bool _isPackageReference(SourceReference reference) {
      var unitSourceContent = reference.element.unitSourceContent;
      if (unitSourceContent == null) {
        return false;
      }
      var quotedImportUri = unitSourceContent.substring(reference.range.offset,
          reference.range.offset + reference.range.length);
      return packagePrefixedStringPattern.hasMatch(quotedImportUri);
    }
  