Add tbansal to selective owner for histograms.xml

Read the slides :)

Change-Id: Ie57099fdcc10fd6ba5c2d69eba85f552892c917e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504492Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638156}

tools/metrics/histograms/OWNERS

@@ -8,6 +8,7 @@ per-file histograms.xml=alexilin@chromium.org
 per-file histograms.xml=csharrison@chromium.org
 per-file histograms.xml=cthomp@chromium.org  # For security-related metrics only.
 per-file histograms.xml=schenney@chromium.org
+per-file histograms.xml=tbansal@chromium.org
 
 per-file histograms.xml=set noparent