public static boolean isClassUsed(@NotNull Project project,
                                    @NotNull PsiFile containingFile,
                                    @NotNull PsiClass aClass,
                                    @NotNull GlobalUsageHelper helper) {
    Boolean result = helper.unusedClassCache.get(aClass);
    if (result == null) {
      result = isReallyUsed(project, containingFile, aClass, helper);
      helper.unusedClassCache.put(aClass, result);
    }
    return result;
  }
public static boolean isClassUsed(@NotNull Project project,
                                    @NotNull PsiFile containingFile,
                                    @NotNull PsiClass aClass,
                                    @NotNull GlobalUsageHelper helper)