[CrOS Settings] Add missing metrics enum for Nearby Share on/off

Was forgotten in the original CL:
https://chromium-review.googlesource.com/c/chromium/src/+/2233898

Bug: b/154866535
Change-Id: I49b7d808ef62c1ebd9537043f1a0e61fc7c7fb08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250472
Auto-Submit: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: James Vecore <vecore@google.com>
Reviewed-by: James Vecore <vecore@google.com>
Cr-Commit-Position: refs/heads/master@{#779673}

tools/metrics/histograms/enums.xml

@@ -51128,6 +51128,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="205" label="Messages: Set Up"/>
   <int value="206" label="Messages: On/Off"/>
   <int value="207" label="Forget Phone"/>
+  <int value="208" label="Nearby Share: On/Off"/>
   <int value="300" label="Add Account"/>
   <int value="301" label="Remove Account"/>
   <int value="302" label="Sync On/Off"/>