Add metrics constant for new settings activity

Bug: 28554048
Change-Id: I3e2008890779867ecbc5fe485f33d52d75f0b324
diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index f6de94f..b7677c6 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -2200,6 +2200,9 @@
     // Settings -> Dev options -> Running services
     RUNNING_SERVICES = 404;
 
+    // The dialog shown by 3P intent to change current webview implementation.
+    WEBVIEW_IMPLEMENTATION = 405;
+
     // Add new aosp constants above this line.
     // END OF AOSP CONSTANTS
   }