[Offline pages] Create offliner that uses background loader

components/offline_pages/content/background_loader/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")
 }
 
 source_set("background_loader") {
   sources = [
     "background_loader_contents.cc",
     "background_loader_contents.h",
   ]
 
   deps = [
     "//content/public/browser",
     "//url",
   ]
 }
 
+source_set("test_support") {
+  testonly = true
+
+  sources = [
+    "background_loader_contents_stub.cc",
+    "background_loader_contents_stub.h",
+  ]
+
+  deps = [
+    ":background_loader",
+    "//content/test:test_support",
+  ]
+}
+
 source_set("unit_tests") {
   testonly = true
   sources = [
     "background_loader_contents_unittest.cc",
   ]
   deps = [
     ":background_loader",
     "//base",
     "//content/test:test_support",
     "//testing/gtest",
   ]
 }