Fix git cl format for actions.xml changes.

Makes tools/metrics/actions follow the convention used in
tools/metrics/histograms and tools/metrics/rappor of having
a pretty_print.py file that formats the XML file. This is what
git cl format expects.

BUG=706501

Review-Url: https://codereview.chromium.org/2786433003
Cr-Commit-Position: refs/heads/master@{#460546}

tools/metrics/actions/pretty_print.py

+#!/usr/bin/env python
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import logging
+import os
+import sys
+
+import extract_actions
+sys.path.append(os.path.join(os.path.dirname(__file__), '..', 'common'))
+import presubmit_util
+
+def main(argv):
+  presubmit_util.DoPresubmitMain(argv, 'actions.xml', 'actions.old.xml',
+                                 'pretty_print.py', extract_actions.UpdateXml)
+
+
+if '__main__' == __name__:
+  sys.exit(main(sys.argv))