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

chrome/common/device_form_factor_ios.mm

+// 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 "device_form_factor.h"
+
+#import <UIKit/UIKit.h>
+
+DeviceFormFactor GetDeviceFormFactor() {
+  UIUserInterfaceIdiom idiom = [[UIDevice currentDevice] userInterfaceIdiom];
+  if (idiom == UIUserInterfaceIdiomPad) {
+    return DEVICE_FORM_FACTOR_TABLET;
+  }
+  return DEVICE_FORM_FACTOR_PHONE;
+}