Add an owner for the "DirectWrite" histograms.

These are all font related histograms so I should own them
as metrics lead for the Blink Rendering Core team.

Change-Id: If7a2ab7fcf5d34810ca8dc5e6f155d3d93a28795
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485302
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Auto-Submit: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819315}

tools/metrics/histograms/histograms_xml/direct/OWNERS

+# If none of these reviewers are available, please send CLs to
+# <chromium-metrics-reviews@google.com>.
+# See tools/metrics/histograms/histograms_xml/OWNERS for details.
+schenney@chromium.org