Handle app custom icon via aura::Window property.

chrome/test/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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 2007 matching lines @@
       deps += [
         "//ash/test:test_support_with_content",
         "//ui/keyboard:test_support",
       ]
 
       if (enable_app_list) {
         deps += [ ":test_support_applist_ash" ]
       }
     }
     if (use_aura) {
-      sources += [ "../browser/ui/aura/accessibility/automation_manager_aura_browsertest.cc" ]
+      sources += [
+        "../browser/ui/aura/accessibility/automation_manager_aura_browsertest.cc",
+        "../browser/ui/test/test_app_window_icon_observer.cc",
+        "../browser/ui/test/test_app_window_icon_observer.h",
+      ]
     }
     if (use_aura || toolkit_views) {
       deps += [ "//ui/events:test_support" ]
     }
     if (toolkit_views) {
       sources += [
         "../browser/payments/site_per_process_payments_browsertest.cc",
         "../browser/ui/global_error/global_error_service_browsertest.cc",
         "../browser/ui/views/bookmarks/bookmark_editor_view_browsertest.cc",
         "../browser/ui/views/extensions/extension_message_bubble_view_browsertest.cc",
@@ skipping 3103 matching lines @@
 }
 
 if (is_win) {
   loadable_module("conflicts_dll") {
     testonly = true
     sources = [
       "conflicts/conflicts_dll.cc",
     ]
   }
 }