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

ui/base/device_form_factor_ios.mm

Index: ui/base/device_form_factor_ios.mm
diff --git a/ui/base/device_form_factor_ios.mm b/ui/base/device_form_factor_ios.mm
new file mode 100644
index 0000000000000000000000000000000000000000..496af18a832b01ac70b7285848bb1fe8940df088
--- /dev/null
+++ b/ui/base/device_form_factor_ios.mm
@@ -0,0 +1,18 @@
+// 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.
+
+#include "ui/base/device_form_factor.h"
+
+#import <UIKit/UIKit.h>
+
+namespace ui {
+
+DeviceFormFactor GetDeviceFormFactor() {
+  UIUserInterfaceIdiom idiom = [[UIDevice currentDevice] userInterfaceIdiom];
+  if (idiom == UIUserInterfaceIdiomPad)
+    return DEVICE_FORM_FACTOR_TABLET;
+  return DEVICE_FORM_FACTOR_PHONE;
+}
+
+} // namespace ui