[Content suggestions] Implement fetching publishers' favicons

ios/chrome/browser/ntp_snippets/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.
 
 source_set("ntp_snippets") {
   sources = [
     "ios_chrome_content_suggestions_service_factory.cc",
     "ios_chrome_content_suggestions_service_factory.h",
   ]
   deps = [
     "//base",
     "//components/bookmarks/browser",
     "//components/image_fetcher/core",
     "//components/image_fetcher/ios",
     "//components/keyed_service/core",
     "//components/keyed_service/ios",
     "//components/ntp_snippets",
     "//components/reading_list/core",
     "//components/signin/core/browser",
     "//components/version_info",
     "//google_apis",
     "//ios/chrome/browser",
     "//ios/chrome/browser/bookmarks",
     "//ios/chrome/browser/browser_state",
+    "//ios/chrome/browser/favicon",
     "//ios/chrome/browser/history",
     "//ios/chrome/browser/reading_list",
     "//ios/chrome/browser/signin",
     "//ios/chrome/common",
     "//ios/web",
     "//net",
   ]
 }