Flip the flag to enable smooth screen rotation by default.

ash/test/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("//build/config/ui.gni")
 
 static_library("test_support_without_content") {
   testonly = true
   sources = [
     "ash_test_environment_default.cc",
@@ skipping 46 matching lines @@
     "../mus/test/ash_test_impl_mus.cc",
     "../mus/test/ash_test_impl_mus.h",
     "../mus/test/wm_test_base.cc",
     "../mus/test/wm_test_base.h",
     "../mus/test/wm_test_helper.cc",
     "../mus/test/wm_test_helper.h",
     "../rotator/test/screen_rotation_animator_test_api.cc",
     "../rotator/test/screen_rotation_animator_test_api.h",
     "../shell/toplevel_window.cc",
     "../shell/toplevel_window.h",
+    "../system/overview/test/overview_button_tray_test_api.cc",
+    "../system/overview/test/overview_button_tray_test_api.h",
     "ash_test.cc",
     "ash_test.h",
     "ash_test_base.cc",
     "ash_test_base.h",
     "ash_test_environment.h",
     "ash_test_helper.cc",
     "ash_test_helper.h",
     "ash_test_impl.h",
     "ash_test_impl_aura.cc",
     "ash_test_impl_aura.h",
@@ skipping 128 matching lines @@
   deps = [
     ":test_support_with_content",
     "//base",
     "//skia",
     "//testing/gtest",
     "//ui/aura",
     "//ui/base",
     "//ui/gl:test_support",
   ]
 }