Add presubmit check and automatic update script for ExtensionPermission enum.

tools/metrics/histograms/update_extension_permission.py

+# Copyright 2014 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.
+
+"""Updates ExtensionPermission2 enum in histograms.xml file with values read
+from permission_message.h.
+
+If the file was pretty-printed, the updated version is pretty-printed too.
+"""
+
+import os
+
+from update_histogram_enum import UpdateHistogramEnum
+
+if __name__ == '__main__':
+  UpdateHistogramEnum(histogram_enum_name='ExtensionPermission2',
+                      source_enum_path=os.path.join('..', '..', '..',
+                                                    'extensions', 'common',
+                                                    'permissions',
+                                                    'permission_message.h'),
+                      start_marker='^enum ID {',
+                      end_marker='^kEnumBoundary')