Add support for GCM subtypes to desktop Instance ID implementation

ios/chrome/browser/application_context_impl.cc

Index: ios/chrome/browser/application_context_impl.cc
diff --git a/ios/chrome/browser/application_context_impl.cc b/ios/chrome/browser/application_context_impl.cc
index 4f7ace27c42356a3cf80bf31b99e06da561a19dd..5f35e1304d95c3e3101d482671e11a54f2ff0212 100644
--- a/ios/chrome/browser/application_context_impl.cc
+++ b/ios/chrome/browser/application_context_impl.cc
@@ -338,6 +338,19 @@ void ApplicationContextImpl::CreateGCMDriver() {
 
   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(
@@ -347,7 +360,8 @@ void ApplicationContextImpl::CreateGCMDriver() {
   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);
 }