Add pause/resume functionality to precache

components/precache/content/BUILD.gn

 # Copyright 2014 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.
 
 source_set("content") {
   sources = [
     "precache_manager.cc",
     "precache_manager.h",
   ]
 
   configs += [ "//components/precache/core:precache_config" ]
 
   deps = [
     "//base",
     "//components/history/core/browser",
     "//components/keyed_service/core",
     "//components/precache/core",
+    "//components/precache/core:proto",
     "//components/prefs",
     "//components/sync_driver",
     "//components/variations",
     "//content/public/browser",
     "//net",
     "//sql",
     "//url",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "precache_manager_unittest.cc",
   ]
   deps = [
     ":content",
     "//base",
     "//base/test:test_support",
     "//components/history/core/browser",
     "//components/precache/core",
+    "//components/precache/core:proto",
     "//content/public/browser",
     "//content/test:test_support",
     "//net:test_support",
     "//sql",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }