Refactor cache counting into a separate helper class

components/browsing_data/content/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 static_library("content") {
   sources = [
+    "conditional_cache_counting_helper.cc",
+    "conditional_cache_counting_helper.h",
     "conditional_cache_deletion_helper.cc",
     "conditional_cache_deletion_helper.h",
     "storage_partition_http_cache_data_remover.cc",
     "storage_partition_http_cache_data_remover.h",
   ]
 
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
     "//base",
     "//content/public/browser",
     "//net",
   ]
 }