Flip the flag to enable smooth screen rotation by default.

ash/system/overview/test/overview_button_tray_test_api.h

Index: ash/system/overview/test/overview_button_tray_test_api.h
diff --git a/ash/system/overview/test/overview_button_tray_test_api.h b/ash/system/overview/test/overview_button_tray_test_api.h
new file mode 100644
index 0000000000000000000000000000000000000000..e7a3504436c66ab1e2df5eafbdfff95cd2ee190f
--- /dev/null
+++ b/ash/system/overview/test/overview_button_tray_test_api.h
@@ -0,0 +1,33 @@
+// Copyright 2017 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_SYSTEM_OVERVIEW_TEST_OVERVIEW_BUTTON_TRAY_TEST_API_H_
+#define ASH_SYSTEM_OVERVIEW_TEST_OVERVIEW_BUTTON_TRAY_TEST_API_H_
+
+#include <stdint.h>
+
+#include "base/macros.h"
+
+namespace ash {
+class OverviewButtonTray;
+
+namespace test {
+
+// Test API to provide internal access to a OverviewButtonTray instance.
+class OverviewButtonTrayTestApi {
+ public:
+  explicit OverviewButtonTrayTestApi(OverviewButtonTray* tray);
+
+  void AbortAllAnimations();
+
+ private:
+  OverviewButtonTray* tray_;
+
+  DISALLOW_COPY_AND_ASSIGN(OverviewButtonTrayTestApi);
+};
+
+}  // namespace test
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_OVERVIEW_TEST_OVERVIEW_BUTTON_TRAY_TEST_API_H_