Move all components/offline_pages/ files into component/offline_pages/core

components/offline_pages/core/request_header/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.
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 static_library("request_header") {
   sources = [
@@ skipping 12 matching lines @@
     "offline_page_header_unittest.cc",
   ]
 
   deps = [
     ":request_header",
     "//base",
     "//base/test:test_support",
     "//testing/gtest",
   ]
 }