Add support for GCM subtypes to desktop Instance ID implementation

components/gcm_driver/instance_id/instance_id_driver.h

Index: components/gcm_driver/instance_id/instance_id_driver.h
diff --git a/components/gcm_driver/instance_id/instance_id_driver.h b/components/gcm_driver/instance_id/instance_id_driver.h
index 38e1e6224b93c61c654b6b376b95d055daccb36e..a55a831a992d869024370b7a7d095aeb58cdd7d8 100644
--- a/components/gcm_driver/instance_id/instance_id_driver.h
+++ b/components/gcm_driver/instance_id/instance_id_driver.h
@@ -30,9 +30,17 @@ class InstanceIDDriver {
   virtual ~InstanceIDDriver();
 
   // Returns the InstanceID that provides the Instance ID service for the given
-  // application. The lifetime of InstanceID will be managed by this class.
+  // application. The lifetime of the InstanceID will be managed by this class.
   InstanceID* GetInstanceID(const std::string& app_id);
 
+  // Like |GetInstanceID|, except that for historical reasons, Chrome Apps and
+  // Extensions send the |app_id| to GCM as a "category" instead of a "subtype".
+  // Not recommended for new code, since this does not (and cannot) support
+  // Android, and switching between this and |GetInstanceID| is not supported (a
+  // given |app_id| must either always use |GetInstanceID| or always use
+  // |GetInstanceIDForExtensions|, even across Chrome versions).
+  InstanceID* GetInstanceIDForExtensions(const std::string& app_id);
+
   // Removes the InstanceID when it is not longer needed, i.e. the app is being
   // uninstalled.
   void RemoveInstanceID(const std::string& app_id);
@@ -42,6 +50,8 @@ class InstanceIDDriver {
   bool ExistsInstanceID(const std::string& app_id) const;
 
  private:
+  InstanceID* GetInstanceID(const std::string& app_id, bool use_subtype);
+
   // Owned by GCMProfileServiceFactory, which is a dependency of
   // InstanceIDProfileServiceFactory, which owns this.
   gcm::GCMDriver* gcm_driver_;