anchor.diff:    void codegen(WorkItem work) { }
     void processNativeClasses(Enqueuer world,
                               Collection<LibraryElement> libraries) { }
  +
  +  bool isUserLibrary(LibraryElement lib) {
  +    final INTERNAL_HELPERS = [
  +      compiler.jsHelperLibrary,
  +      compiler.interceptorsLibrary,
  +    ];
  +    return INTERNAL_HELPERS.indexOf(lib) == -1 && !lib.isPlatformLibrary;
  +  }
   
     void assembleProgram() {
       // Conservatively traverse all platform libraries and collect member names.
  
positive.code:      * Tells whether we should output given element. Corelib classes like
       * Object should not be in the resulting code.
       */
      final LIBS_TO_IGNORE = [
        compiler.jsHelperLibrary,
        compiler.interceptorsLibrary,
      ];
      bool shouldOutput(Element element) =>
        element.kind !== ElementKind.VOID &&
        LIBS_TO_IGNORE.indexOf(element.getLibrary()) == -1 &&
        !element.getLibrary().isPlatformLibrary &&
        element is !SynthesizedConstructorElement &&
        element is !AbstractFieldElement;
  
  
negative.code:     final unparser = new Unparser.withRenamer((Node node) => renames[node]);
      emitCode(unparser, imports, topLevelNodes, memberNodes);
      compiler.assembledCode = unparser.result;
  
      // Output verbose info about size ratio of resulting bundle to all
      // referenced non-platform sources.
      logResultBundleSizeInfo(topLevelElements);
    }
  
    void logResultBundleSizeInfo(Set<Element> topLevelElements) {
      Collection<LibraryElement> referencedLibraries =
          compiler.libraries.getValues().filter(isUserLibrary);
      // Sum total size of scripts in each referenced library.
      int nonPlatformSize = 0;
      for (LibraryElement lib in referencedLibraries) {
        for (CompilationUnitElement compilationUnit in lib.compilationUnits) {
          nonPlatformSize += compilationUnit.script.text.length;
        }
      }
      int percentage = compiler.assembledCode.length * 100 ~/ nonPlatformSize;
      log('Total used non-platform files size: ${nonPlatformSize} bytes, '
          'bundle size: ${compiler.assembledCode.length} bytes (${percentage}%)');
    }
  
    log(String message) => compiler.log('[DartBackend] $message');
  