Add metrics event for Settings->Display->Ambient Display.

Bug: 29994493
Change-Id: I2eb71063db254cbe92511ca5cbe93b32c6b2c601
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index d9f2bac..5099db7 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -2203,6 +2203,10 @@
     // System navigation key down.
     ACTION_SYSTEM_NAVIGATION_KEY_DOWN = 494;
 
+    // OPEN: Settings > Display -> Ambient Display
+    // CATEGORY: SETTINGS
+    ACTION_AMBIENT_DISPLAY = 495;
+
     // ---- End N-MR1 Constants, all N-MR1 constants go above this line ----
     // Add new aosp constants above this line.
     // END OF AOSP CONSTANTS