anchor.diff:        '$sdkRoot/lib/_internal/internal.dart',
         '''
   library dart._internal;
  +
   class Symbol {}
  +
   class ExternalName {
     final String name;
     const ExternalName(this.name);
  
positive.code: }
  
  class IFrameElement extends HtmlElement {
    factory IFrameElement._() { throw new UnsupportedError("Not supported"); }
    factory IFrameElement() => JS(
        'returns:IFrameElement;creates:IFrameElement;new:true',
        '#.createElement(#)',
  
negative.code: 
    final AnalysisOptionsImpl _analysisOptions;
  
    /// The [AnalysisContextImpl] which is used for all of the sources.
    AnalysisContextImpl _analysisContext;
  
    @override
    final List<SdkLibrary> sdkLibraries = [];
  
    /// The cached linked bundle of the SDK.
    PackageBundle _bundle;
  
    /// Optional [additionalLibraries] should have unique URIs, and paths in
  