anchor.diff:  
     @override
     List<ImportElement> getImportsWithPrefix(PrefixElement prefixElement) {
  -    var imports = this.imports;
  -    int count = imports.length;
  -    List<ImportElement> importList = new List<ImportElement>();
  -    for (int i = 0; i < count; i++) {
  -      if (identical(imports[i].prefix, prefixElement)) {
  -        importList.add(imports[i]);
  -      }
  -    }
  -    return importList;
  +    return getImportsWithPrefixFromImports(prefixElement, imports);
     }
   
     @override
     ClassElement getType(String className) {
  -    ClassElement type = _definingCompilationUnit.getType(className);
  -    if (type != null) {
  -      return type;
  -    }
  -    for (CompilationUnitElement part in _parts) {
  -      type = part.getType(className);
  -      if (type != null) {
  -        return type;
  -      }
  -    }
  -    return null;
  +    return getTypeFromParts(className, _definingCompilationUnit, _parts);
     }
   
     /** Given an update to this library which may have added or deleted edges
  
positive.code:     return prefixes.toList(growable: false);
    }
  
    /**
     * Return the [LibraryElementImpl] of the given [element].
     */
  
negative.code:       return getImpl(element.actualElement);
      }
      return element as LibraryElementImpl;
    }
  
    static List<ImportElement> getImportsWithPrefixFromImports(
        PrefixElement prefixElement, List<ImportElement> imports) {
      int count = imports.length;
      List<ImportElement> importList = new List<ImportElement>();
      for (int i = 0; i < count; i++) {
        if (identical(imports[i].prefix, prefixElement)) {
          importList.add(imports[i]);
        }
      }
      return importList;
    }
  
    static ClassElement getTypeFromParts(
        String className,
        CompilationUnitElement definingCompilationUnit,
        List<CompilationUnitElement> parts) {
      ClassElement type = definingCompilationUnit.getType(className);
      if (type != null) {
        return type;
      }
      for (CompilationUnitElement part in parts) {
        type = part.getType(className);
        if (type != null) {
          return type;
        }
      }
      return null;
    }
  
    /**
  