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

ios/chrome/browser/physical_web/physical_web_prefs_registration.h

Index: ios/chrome/browser/physical_web/physical_web_prefs_registration.h
diff --git a/ios/chrome/browser/physical_web/physical_web_prefs_registration.h b/ios/chrome/browser/physical_web/physical_web_prefs_registration.h
new file mode 100644
index 0000000000000000000000000000000000000000..c18f4a8cf92abcaaec295979d9e0e57d8d636298
--- /dev/null
+++ b/ios/chrome/browser/physical_web/physical_web_prefs_registration.h
@@ -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.
+
+#ifndef IOS_CHROME_BROWSER_PHYSICAL_WEB_PHYSICAL_WEB_PREFS_REGISTRATION_H_
+#define IOS_CHROME_BROWSER_PHYSICAL_WEB_PHYSICAL_WEB_PREFS_REGISTRATION_H_
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
+// Registers the prefs needed by physical web.
+void RegisterPhysicalWebBrowserStatePrefs(
+    user_prefs::PrefRegistrySyncable* registry);
+
+#endif  // IOS_CHROME_BROWSER_PHYSICAL_WEB_PHYSICAL_WEB_PREFS_REGISTRATION_H_