Add git cl format support for "structured" metrics

This matches the support for the other metrics subdirectories.

R=ehmaldonado@chromium.org

Bug: none
Change-Id: Ibf84e1d1b33e38843b8a11ff3299d4c0c3aa5eb2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2173743
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Ilya Sherman <isherman@chromium.org>

git_cl.py

@@ -4998,6 +4998,7 @@ def GetDirtyMetricsDirs(diff_files):
     os.path.join('tools', 'metrics', 'actions'),
     os.path.join('tools', 'metrics', 'histograms'),
     os.path.join('tools', 'metrics', 'rappor'),
+    os.path.join('tools', 'metrics', 'structured'),
     os.path.join('tools', 'metrics', 'ukm'),
   ]
   for xml_dir in metrics_xml_dirs: