[profile-menu] Add missing histogram enum entry

... for the sync settings button.

Bug: 995720
Change-Id: Ibe4116fb350730c616821164c36791a73a3a302a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1831797
Auto-Submit: Thomas Tangl <tangltom@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701054}

tools/metrics/histograms/enums.xml

@@ -50463,6 +50463,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="13" label="Switch to another profile button"/>
   <int value="14" label="Cookies cleared on exit link"/>
   <int value="15" label="Add new profile button"/>
+  <int value="16" label="Sync settings(sync on) button"/>
 </enum>
 
 <enum name="ProfileNetUserCount">