Add support for GCM subtypes to desktop Instance ID implementation

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 6c581acde1d210eda620d52870d9284332459f1a..cedf6af7902b880c547b4e0564b9b951296a7c71 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1224,6 +1224,11 @@ const char kPushMessagingAppIdentifierMap[] =
 // Maps from origin to background budget information.
 const char kBackgroundBudgetMap[] = "push_messaging.background_budget_map";
 
+// 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.
+const char kGCMProductCategoryForSubtypes[] =
+    "gcm.product_category_for_subtypes";
+
 // Whether a user is allowed to use Easy Unlock.
 const char kEasyUnlockAllowed[] = "easy_unlock.allowed";