Add launcher metrics for tracking kids nav mode change events.

Fix: 241762670
Test: wwdebug && wwlogcat
Change-Id: I24432f2cd0dddbcc5991645b60a1a8e91dc431e5
diff --git a/protos/launcher_atom.proto b/protos/launcher_atom.proto
index 10eedc8..151ec5a 100644
--- a/protos/launcher_atom.proto
+++ b/protos/launcher_atom.proto
@@ -45,6 +45,9 @@
 
   // Stores the origin of the Item
   repeated Attribute item_attributes = 12;
+
+  // Stores whether the navigation bar is in kids mode.
+  optional bool is_kids_mode = 13;
 }
 
 message LauncherAttributes{