Make ui gn check pass. Misc GN build improvements.

ui/app_list/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.
 
 import("//build/config/ui.gni")
 
 component("app_list") {
   sources = [
     "app_list_constants.cc",
     "app_list_constants.h",
@@ skipping 40 matching lines @@
     "speech_ui_model_observer.h",
   ]
 
   defines = [ "APP_LIST_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//base:i18n",
     "//base/third_party/dynamic_annotations",
     "//skia",
+    "//sync",
     "//third_party/icu",
     "//ui/accessibility",
     "//ui/base",
     "//ui/compositor",
     "//ui/events:events_base",
     "//ui/gfx",
     "//ui/gfx/geometry",
     "//ui/resources",
     "//ui/strings",
   ]
@@ skipping 169 matching lines @@
       "cocoa/app_list_view_controller_unittest.mm",
       "cocoa/app_list_window_controller_unittest.mm",
       "cocoa/apps_grid_controller_unittest.mm",
       "cocoa/apps_search_box_controller_unittest.mm",
       "cocoa/apps_search_results_controller_unittest.mm",
       "cocoa/test/apps_grid_controller_test_helper.h",
       "cocoa/test/apps_grid_controller_test_helper.mm",
     ]
   }
 }