Add support for GCM subtypes to desktop Instance ID implementation

chrome/browser/services/gcm/gcm_product_util.cc

+// 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 "chrome/browser/services/gcm/gcm_product_util.h"
+
+#include "base/strings/string_piece.h"
+#include "base/strings/string_util.h"
+#include "chrome/common/channel_info.h"
+#include "chrome/common/chrome_version.h"
+#include "chrome/common/pref_names.h"
+#include "components/pref_registry/pref_registry_syncable.h"
+#include "components/prefs/pref_service.h"
+#include "components/version_info/version_info.h"
+
+namespace gcm {
+
+namespace {
+
+std::string ToLowerAlphaNum(base::StringPiece in) {
+  std::string out;
+  out.reserve(in.size());
+  for (size_t i = 0; i < in.size(); i++) {

[Peter Beverloo, 2016/07/28 12:34:09]

nit: can modernize and reduce indexed array access by using a c++11 for.

[johnme, 2016/08/04 17:47:13]

Done. Serve me right for copy-pasting from base/ :p

+    if (base::IsAsciiAlpha(in[i]) || base::IsAsciiDigit(in[i]))
+      out.push_back(base::ToLowerASCII(in[i]));
+  }
+  return out;
+}
+
+}  // namespace
+
+// Returns a string like "com.chrome.stable.macosx" that should be used as the
+// 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 CategoryForSubtypes(PrefService* prefs) {
+  std::string category_for_subtypes =
+      prefs->GetString(prefs::kGCMCategoryForSubtypes);
+  if (!category_for_subtypes.empty())
+    return category_for_subtypes;
+
+  std::string product = ToLowerAlphaNum(PRODUCT_SHORTNAME_STRING);
+  std::string ns = product == "chromium" ? "org" : "com";

[Peter Beverloo, 2016/07/28 12:34:09]

This still feels wrong to me, but I don't know what else to suggest :-(. I guess
it'll work in the 80% case..

[johnme, 2016/08/04 17:47:14]

Acknowledged. Since this is now in the chrome/ layer, it's reasonable to expect
that non-Chrome embedders will fork this anyway.

+  std::string channel =
+      ToLowerAlphaNum(version_info::GetChannelString(chrome::GetChannel()));
+  std::string platform = ToLowerAlphaNum(version_info::GetOSType());
+  category_for_subtypes = ns + '.' + product + '.' + channel + '.' + platform;
+
+  prefs->SetString(prefs::kGCMCategoryForSubtypes, category_for_subtypes);
+  return category_for_subtypes;
+}
+
+void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry) {
+  registry->RegisterStringPref(prefs::kGCMCategoryForSubtypes,
+                               std::string() /* default_value */);
+}
+
+}  // namespace gcm