Send both system id and product id to Omaha.

The request will have two <app> with different app_id and version.

Test: observe request in the log
Change-Id: I51b0dcf3c0affc81fe152ff24ce0ccc9a36e6385
(cherry picked from commit 573919d54a8421f1b2147d801ae4104adebf5cd7)
diff --git a/omaha_request_params.h b/omaha_request_params.h
index 3a28ed1..cdc5f38 100644
--- a/omaha_request_params.h
+++ b/omaha_request_params.h
@@ -109,6 +109,7 @@
   inline std::string canary_app_id() const {
     return image_props_.canary_product_id;
   }
+  inline std::string system_app_id() const { return image_props_.system_id; }
   inline void set_app_id(const std::string& app_id) {
     image_props_.product_id = app_id;
     image_props_.canary_product_id = app_id;
@@ -122,6 +123,9 @@
     image_props_.version = version;
   }
   inline std::string app_version() const { return image_props_.version; }
+  inline std::string system_version() const {
+    return image_props_.system_version;
+  }
 
   inline std::string current_channel() const {
     return image_props_.current_channel;