Create a UKM descriptions XML file

tools/metrics/ukm/PRESUBMIT.py

Index: tools/metrics/ukm/PRESUBMIT.py
diff --git a/tools/metrics/ukm/PRESUBMIT.py b/tools/metrics/ukm/PRESUBMIT.py
new file mode 100644
index 0000000000000000000000000000000000000000..41c542693e7c10a7cf744c2cf344bbb3a91ee622
--- /dev/null
+++ b/tools/metrics/ukm/PRESUBMIT.py
@@ -0,0 +1,35 @@
+# 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.
+
+"""Presubmit script for ukm.xml.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
+for more details on the presubmit API built into gcl.
+"""
+
+UKM_XML = 'ukm.xml'
+
+
+def CheckChange(input_api, output_api):
+  """Checks that ukm.xml is pretty-printed and well-formatted."""
+  for f in input_api.AffectedTextFiles():
+    p = f.AbsoluteLocalPath()
+    if (input_api.basename(p) == UKM_XML
+        and input_api.os_path.dirname(p) == input_api.PresubmitLocalPath()):
+      cwd = input_api.os_path.dirname(p)
+      exit_code = input_api.subprocess.call(
+          ['python', 'pretty_print.py', '--presubmit'], cwd=cwd)
+      if exit_code != 0:
+        return [output_api.PresubmitError(
+            '%s is not formatted correctly; run %s/pretty_print.py to fix' %
+            (UKM_XML, input_api.PresubmitLocalPath()))]
+  return []
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return CheckChange(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return CheckChange(input_api, output_api)