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 92fbcc38d05fee9e5e3d5175b9308d6224f7c1c5..d9e4633031462ded890c03e0af1d4d7405333a6c 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -1224,6 +1224,10 @@ 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 kGCMCategoryForSubtypes[] = "gcm.category_for_subtypes";
+
 // Whether a user is allowed to use Easy Unlock.
 const char kEasyUnlockAllowed[] = "easy_unlock.allowed";