Add wrapper for logging backup & restore metrics from Launcher

Bug: 25177913
Flag: ACONFIG com.android.launcher3.enable_launcher_br_metrics DEVELOPMENT
Test: locally

Change-Id: I220721f705eb7244a1f13ef8997682999d799f51
diff --git a/res/values/config.xml b/res/values/config.xml
index 154312a..2980635 100644
--- a/res/values/config.xml
+++ b/res/values/config.xml
@@ -86,6 +86,7 @@
     <string name="widget_holder_factory_class" translatable="false"></string>
     <string name="taskbar_search_session_controller_class" translatable="false"></string>
     <string name="taskbar_model_callbacks_factory_class" translatable="false"></string>
+    <string name="launcher_restore_event_logger_class" translatable="false"></string>
 
     <!-- View ID to use for QSB widget -->
     <item type="id" name="qsb_widget" />