anchor.diff:        '$sdkRoot/lib/html/dart2js/html_dart2js.dart',
         '''
   library dart.dom.html;
  +
   import 'dart:async';
   
   class Event {}
  +
   class MouseEvent extends Event {}
  +
   class FocusEvent extends Event {}
  +
   class KeyEvent extends Event {}
   
   abstract class ElementStream<T extends Event> implements Stream<T> {}
  
positive.code: 
  const double E = 2.718281828459045;
  const double PI = 3.1415926535897932;
  const double LN10 =  2.302585092994046;
  
  T min<T extends num>(T a, T b) => throw 0;
  T max<T extends num>(T a, T b) => throw 0;
  
negative.code:     return null;
    }
  
    /// Compute the bytes of the linked bundle associated with this SDK.
    List<int> _computeLinkedBundleBytes() {
      List<Source> librarySources = sdkLibraries
          .map((SdkLibrary library) => mapDartUri(library.shortName))
  