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 91ed2ee881d88f7fe0f7540eef4bef7a4d0e925a..d63572e121166b6a7e9a824144787084eff8a1bc 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.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";