Add cross-platform API to get the form factor of the device

ui/base/device_form_factor.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 UI_BASE_DEVICE_FORM_FACTOR_H_
+#define UI_BASE_DEVICE_FORM_FACTOR_H_
+
+#include "ui/base/ui_export.h"
+
+namespace ui {
+
+enum DeviceFormFactor {
+  DEVICE_FORM_FACTOR_DESKTOP = 0,
+  DEVICE_FORM_FACTOR_PHONE = 1,
+  DEVICE_FORM_FACTOR_TABLET = 2
+};
+
+// Returns the form factor of current device. For platforms other than Android
+// and iOS, DEVICE_FORM_FACTOR_DESKTOP is always returned.
+UI_EXPORT DeviceFormFactor GetDeviceFormFactor();
+
+}  // namespace ui
+
+#endif  // UI_BASE_DEVICE_FORM_FACTOR_H_