Add test for ash devtools DOM agent getDocument method

ash/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/features.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//ui/base/ui_features.gni")
 
 assert(use_aura)
@@ skipping 1191 matching lines @@
   sources = [
     "accelerators/accelerator_commands_unittest.cc",
     "accelerators/accelerator_controller_unittest.cc",
     "accelerators/accelerator_filter_unittest.cc",
     "accelerators/magnifier_key_scroller_unittest.cc",
     "accelerators/spoken_feedback_toggler_unittest.cc",
     "app_list/app_list_presenter_delegate_unittest.cc",
     "ash_touch_exploration_manager_chromeos_unittest.cc",
     "aura/pointer_watcher_adapter_unittest.cc",
     "autoclick/autoclick_unittest.cc",
+    "common/devtools/ash_devtools_unittest.cc",
 
     # TODO: convert to use AshTest http://crbug.com/654489.
     "common/frame/caption_buttons/frame_caption_button_container_view_unittest.cc",
     "common/frame/custom_frame_view_ash_unittest.cc",
     "common/frame/default_header_painter_unittest.cc",
 
     # TODO: convert to use AshTest http://crbug.com/654491.
     "common/material_design/material_design_controller_unittest.cc",
 
     # TODO: convert to use AshTest http://crbug.com/654492.
@@ skipping 278 matching lines @@
   if (is_win) {
     configs -= [ "//build/config/win:console" ]
     configs += [ "//build/config/win:windowed" ]
     deps += [ "//sandbox" ]
   }
 
   if (is_chromeos) {
     deps += [ "//device/bluetooth" ]
   }
 }