Add support for GCM subtypes to desktop Instance ID implementation

ios/chrome/browser/application_context_impl.cc

 // Copyright 2014 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/application_context_impl.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 320 matching lines @@
         local_state_->GetBoolean(prefs::kLastSessionExitedCleanly);
   }
 }
 
 void ApplicationContextImpl::CreateGCMDriver() {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!gcm_driver_);
 
   base::FilePath store_path;
   CHECK(PathService::Get(ios::DIR_GLOBAL_GCM_STORE, &store_path));
+
+// These strings must never change during the lifetime of a Chrome install,
+// since e.g. to unregister an Instance ID token we must pass the same
+// category to FCM as we originally passed when registering it.

[Peter Beverloo, 2016/07/28 12:34:10]

nit: avoid "we" here too (2x)

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

Done.

+#if defined(GOOGLE_CHROME_BUILD)
+  std::string channel = ::GetChannelString();
+  if (channel.empty())
+    channel = "stable";
+  std::string category_for_subtypes = "com.chrome." + channel + ".ios";
+#else
+  std::string category_for_subtypes = "org.chromium.unknown.ios";
+#endif
+
   base::SequencedWorkerPool* worker_pool = web::WebThread::GetBlockingPool();
   scoped_refptr<base::SequencedTaskRunner> blocking_task_runner(
       worker_pool->GetSequencedTaskRunnerWithShutdownBehavior(
           worker_pool->GetSequenceToken(),
           base::SequencedWorkerPool::SKIP_ON_SHUTDOWN));
 
   gcm_driver_ = gcm::CreateGCMDriverDesktop(
       base::WrapUnique(new gcm::GCMClientFactory), GetLocalState(), store_path,
       GetSystemURLRequestContext(), ::GetChannel(),
-      web::WebThread::GetTaskRunnerForThread(web::WebThread::UI),
+      category_for_subtypes web::WebThread::GetTaskRunnerForThread(
+          web::WebThread::UI),
       web::WebThread::GetTaskRunnerForThread(web::WebThread::IO),
       blocking_task_runner);
 }