Reland Mus Demo: Move definition of WindowTreeData into separate files

services/ui/demo/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.
 
 import("//services/catalog/public/tools/catalog.gni")
 import("//services/service_manager/public/cpp/service.gni")
 import("//services/service_manager/public/service_manifest.gni")
 import("//services/service_manager/public/tools/test/service_test.gni")
 import("//testing/test.gni")
 
 source_set("lib") {
   sources = [
     "mus_demo.cc",
     "mus_demo.h",
+    "window_tree_data.cc",
+    "window_tree_data.h",
   ]
 
   public_deps = [
     "//services/service_manager/public/cpp:sources",
     "//skia",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/bindings",
@@ skipping 62 matching lines @@
 }
 
 catalog("mus_demo_unittests_catalog") {
   embedded_services = [ ":test_manifest" ]
 
   standalone_services = [
     ":manifest",
     "//services/ui:manifest",
   ]
 }