Add enums for "Turn on/off" of feed.

Bug: 1122409
Change-Id: I2f732f6ec8344dd0c91ed2935d1e8d434e425503
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2385756
Commit-Queue: Jonathan Freed <freedjm@chromium.org>
Auto-Submit: Jonathan Freed <freedjm@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803172}

tools/metrics/histograms/enums.xml

@@ -29324,6 +29324,8 @@ Called by update_feature_policy_enum.py.-->
   <int value="13"
       label="Ephemeral change undone, likely due to pressing 'undo' on the
              snackbar"/>
+  <int value="14" label="Turn on"/>
+  <int value="15" label="Turn off"/>
   <int value="16" label="Tapped Manage Activity"/>
 </enum>