anchor.diff:  
     @override
     js_ast.Expression visitPropertyGet(PropertyGet node) {
  -    var propertyGet =
  -        _emitPropertyGet(node.receiver, node.interfaceTarget, node.name.text);
  -    if (_isCheckableNative(node.interfaceTarget)) {
  -      // If target is a native getter with a non-nullable type, add a null check
  -      // for soundness.
  -      return runtimeCall('checkNativeNonNull(#)', [propertyGet]);
  -    }
  -    return propertyGet;
  +    return _emitPropertyGet(
  +        node.receiver, node.interfaceTarget, node.name.text);
     }
   
     @override
  
positive.code:   }
  
    /// Return whether [member] returns a native object whose type needs to be
    /// checked.
    bool _isCheckableNative(Member member) =>
        member != null &&
        member.isExternal &&
        _extensionTypes.isNativeClass(member.enclosingClass) &&
  
negative.code:       // Fields on a native class are implicitly native.
        // Methods/getters/setters are marked external/native.
        if (member is Field || _isExternal(member)) {
          // If the native member needs to be null-checked, we require symbolizing
          // it in order to access the null-check at the member definition.
          if (_isNullCheckableNative(member)) return true;
          var jsName = _annotationName(member, isJSName);
          return jsName != null && jsName != name;
        } else {
  