[ios] Adds a helper function to register prefs for Physical Web.

ios/chrome/browser/physical_web/physical_web_prefs_registration.cc

Index: ios/chrome/browser/physical_web/physical_web_prefs_registration.cc
diff --git a/ios/chrome/browser/physical_web/physical_web_prefs_registration.cc b/ios/chrome/browser/physical_web/physical_web_prefs_registration.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8f94b9b6b568b336a37bfb3366eee4bde2a4e0a5
--- /dev/null
+++ b/ios/chrome/browser/physical_web/physical_web_prefs_registration.cc
@@ -0,0 +1,16 @@
+// Copyright 2016 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 "ios/chrome/browser/physical_web/physical_web_prefs_registration.h"
+
+#include "components/pref_registry/pref_registry_syncable.h"
+#include "ios/chrome/browser/physical_web/physical_web_constants.h"
+#include "ios/chrome/browser/pref_names.h"
+
+void RegisterPhysicalWebBrowserStatePrefs(
+    user_prefs::PrefRegistrySyncable* registry) {
+  registry->RegisterIntegerPref(
+      prefs::kIosPhysicalWebEnabled, physical_web::kPhysicalWebOnboarding,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+}