Add a footer item for the Content Suggestions

ios/chrome/browser/ui/content_suggestions/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("content_suggestions") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "content_suggestion.h",
     "content_suggestion.mm",
     "content_suggestion_identifier.h",
     "content_suggestion_identifier.mm",
     "content_suggestions_article_item.h",
     "content_suggestions_article_item.mm",
     "content_suggestions_collection_updater.h",
     "content_suggestions_collection_updater.mm",
     "content_suggestions_commands.h",
     "content_suggestions_data_sink.h",
     "content_suggestions_data_source.h",
     "content_suggestions_expandable_item.h",
     "content_suggestions_expandable_item.mm",
     "content_suggestions_favicon_internal_cell.h",
     "content_suggestions_favicon_internal_cell.mm",
     "content_suggestions_favicon_item.h",
     "content_suggestions_favicon_item.mm",
+    "content_suggestions_footer_item.h",
+    "content_suggestions_footer_item.mm",
     "content_suggestions_image_fetcher.h",
     "content_suggestions_section_information.h",
     "content_suggestions_section_information.mm",
     "content_suggestions_stack_item.h",
     "content_suggestions_stack_item.mm",
     "content_suggestions_stack_item_actions.h",
     "content_suggestions_text_item.h",
     "content_suggestions_text_item.mm",
     "content_suggestions_text_item_actions.h",
     "content_suggestions_view_controller.h",
@@ skipping 16 matching lines @@
 }
 
 source_set("unit_tests") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "content_suggestion_identifier_unittest.mm",
     "content_suggestions_article_item_unittest.mm",
     "content_suggestions_expandable_item_unittest.mm",
     "content_suggestions_favicon_item_unittest.mm",
+    "content_suggestions_footer_item_unittest.mm",
     "content_suggestions_stack_item_unittest.mm",
     "content_suggestions_text_item_unittest.mm",
   ]
   deps = [
     ":content_suggestions",
     "//base",
     "//ios/chrome/browser/ui/collection_view",
     "//testing/gtest",
     "//third_party/ocmock",
     "//url",
   ]
 }