Flip the flag to enable smooth screen rotation by default.

ash/test/ash_test_helper.h

 // Copyright 2013 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.
 
 #ifndef ASH_TEST_ASH_TEST_HELPER_H_
 #define ASH_TEST_ASH_TEST_HELPER_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <utility>
 #include <vector>
 
 #include "ash/test/test_session_controller_client.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/test/scoped_command_line.h"
 #include "ui/aura/test/mus/test_window_tree_client_setup.h"
 
 namespace aura {
 class Window;
 class WindowTreeClientPrivate;
 }
 
 namespace display {
 class Display;
 }
@@ skipping 83 matching lines @@
   }
 
   TestSessionControllerClient* test_session_controller_client() {
     return session_controller_client_.get();
   }
   void set_test_session_controller_client(
       std::unique_ptr<TestSessionControllerClient> session_controller_client) {
     session_controller_client_ = std::move(session_controller_client);
   }
 
+  void reset_commandline() { command_line_.reset(); }
+
  private:
   // These TestSuites need to manipulate |config_|.
   friend class AshTestSuite;
   friend class mash::test::MashTestSuite;
 
   // Called when running in mash to create the WindowManager.
   void CreateMashWindowManager();
 
   // Called when running in ash to create Shell.
   void CreateShell();
@@ skipping 31 matching lines @@
   aura::TestWindowTreeClientSetup window_tree_client_setup_;
   std::unique_ptr<mus::WindowManagerApplication> window_manager_app_;
   std::unique_ptr<aura::WindowTreeClientPrivate> window_tree_client_private_;
   // Id for the next Display created by CreateRootWindowController().
   int64_t next_display_id_ = 1;
 
   std::unique_ptr<TestSessionControllerClient> session_controller_client_;
 
   std::unique_ptr<ui::InputDeviceClient> input_device_client_;
 
+  std::unique_ptr<base::test::ScopedCommandLine> command_line_;
+
   DISALLOW_COPY_AND_ASSIGN(AshTestHelper);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_TEST_ASH_TEST_HELPER_H_