Move the test template to //testing/test.gni (part 2)

mojo/services/view_manager/public/cpp/tests/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")
+import("//testing/test.gni")
 
 test("mojo_view_manager_lib_unittests") {
   sources = [
     "view_unittest.cc",
     "view_manager_unittest.cc",
   ]
 
   deps = [
     "//base",
     "//base/test:test_support",
     "//mojo/converters/geometry",
     "//mojo/environment:chromium",
     "//mojo/public/cpp/application",
     "//mojo/services/geometry/public/cpp",
     "//mojo/services/geometry/public/interfaces",
     "//mojo/services/view_manager/public/cpp",
     "//mojo/services/view_manager/public/cpp/lib:run_unittests",
     "//mojo/services/view_manager/public/interfaces",
     "//shell/application_manager",
     "//shell:test_support",
     "//testing/gtest",
   ]
 }