Also Pretty print the split histogram_suffixes_list

The split histogram_suffies_list.xml should also be pretty-printed via
`git cl format`.

Bug: 1121852
Change-Id: Id9eacdd4adda8a4e6684be4c88dd0d5b0ab033a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2376986
Auto-Submit: Weilun Shi <sweilun@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>

git_cl.py

@@ -5055,8 +5055,9 @@ def CMDformat(parser, args):
       filepath_required = os.path.exists(
           os.path.join(tool_dir, 'validate_prefix.py'))
 
-      if (diff_xml.endswith('histograms.xml')
-          or diff_xml.endswith('enums.xml')) and filepath_required:
+      if (diff_xml.endswith('histograms.xml') or diff_xml.endswith('enums.xml')
+          or diff_xml.endswith('histogram_suffixes_list.xml')
+          ) and filepath_required:
         cmd.append(diff_xml)
 
       if opts.dry_run or opts.diff: