Add support for GCM subtypes to desktop Instance ID implementation

chrome/browser/services/gcm/gcm_product_util.h

+// 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 CHROME_BROWSER_SERVICES_GCM_GCM_PRODUCT_UTIL_H_
+#define CHROME_BROWSER_SERVICES_GCM_GCM_PRODUCT_UTIL_H_
+
+#include <string>
+
+class PrefRegistrySimple;
+class PrefService;
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
+namespace gcm {
+
+// Returns a string like "com.chrome.stable.macosx" that should be used as the

[jianli, 2016/08/17 21:12:07]

Even we need to use same category after channel change, having the old channel
name in the category sounds very confusing when we examine the data usages. Can
we skip those flexible parts? We can still keep os.

[johnme, 2016/08/18 17:43:21]

Done (The assumption was that most users wouldn't change channel, but thinking
about it further I'm not longer sure that's true - a significant fraction of
beta/dev users probably did switch channels from another channel. So I've
removed the channel as suggested. I kept product_shortname though, as that
shouldn't change often, and even if it does the old name will still be useful -
unlike channel, where a wrong channel can be misleading).

+// GCM category when an app_id is sent as a subtype instead of as a category.
+// This is generated once, then remains fixed forever (even if e.g. the product
+// name or channel change), since it must match existing Instance ID tokens.
+std::string GetProductCategoryForSubtypes(PrefService* prefs);
+
+void RegisterPrefs(PrefRegistrySimple* registry);
+void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+
+}  // namespace gcm
+
+#endif  // CHROME_BROWSER_SERVICES_GCM_GCM_PRODUCT_UTIL_H_