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 d3a8501a50ebb30251af37090f9ce41dce4e864a..3cd48c2a54afe423a6a591449632834873088fda 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1233,6 +1233,11 @@ 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";