Update comment for ASSIST_GESTURE_TRIGGERED

Bug: 37874460

Test: make -j56
Change-Id: Idbe9d3b3dfb0e3a2a6c4c66baa44d078e0cb15cb
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index 8d7afc2..7a31fa7 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -4043,6 +4043,7 @@
     ASSIST_GESTURE_PRIMED = 998;
 
     // ACTION: Assist gesture triggered
+    //  SUBTYPE: 1 is for SCREEN_ON, 2 is for SCREEN_OFF
     // CATEGORY: GLOBAL_SYSTEM_UI
     // OS: O DR
     ASSIST_GESTURE_TRIGGERED = 999;