Add support for GCM subtypes to desktop Instance ID implementation

components/gcm_driver/fake_gcm_client.cc

Index: components/gcm_driver/fake_gcm_client.cc
diff --git a/components/gcm_driver/fake_gcm_client.cc b/components/gcm_driver/fake_gcm_client.cc
index 8c6ec7c91227ed88f9fd56513f2c6d027cc64d66..eaa66c894d182fea831ea919e8b275cdc9edd992 100644
--- a/components/gcm_driver/fake_gcm_client.cc
+++ b/components/gcm_driver/fake_gcm_client.cc
@@ -80,6 +80,8 @@ void FakeGCMClient::Initialize(
         url_request_context_getter,
     std::unique_ptr<Encryptor> encryptor,
     Delegate* delegate) {
+  product_category_for_subtypes_ =
+      chrome_build_info.product_category_for_subtypes;
   delegate_ = delegate;
 }