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 ExtensionPermission 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 re
+
+from update_histogram_enum import UpdateHistogramEnum
+
+def StyleLabel(label):
+  '''Transforms labels of form "kLabelName" to "LABEL_NAME"

[Ilya Sherman, 2014/03/10 22:21:54]

Why is this transformation useful?  Why not just use labels of the form
kLabelName? 

[ahernandez, 2014/03/13 19:11:25]

The ExtensionPermission enum already has it's entries styled as LABEL_NAME,
which is why I am preserving that style. If it is better to keep the style as
found in the permission_message.h enum, then that is an easy change to make

+  '''
+  uiIndex = label.find('UI')
+  pattern = '([A-Z])'
+
+  assert label.startswith('k') and label[1].isupper()
+
+  if uiIndex != -1 and label[uiIndex - 1].islower():
+    pattern = '([A-HJ-Z])'

[Jeffrey Yasskin, 2014/03/10 20:53:23]

This looks flaky: Consider (and test!) "kUIWasIsolated" or similar. What's the
actual pattern you're going for? That contiguous capitals should be treated as
acronyms and kept together? Consider using something like
re.finditer([A-Z][a-z]*) and adding onto the result manually.

+
+  return label[1] + re.sub(pattern, r'_\1', label[2:]).upper()
+
+if __name__ == '__main__':
+  UpdateHistogramEnum(histogram_enum_name='ExtensionPermission',
+                      source_enum_path=('../../../extensions/common/permissions'

[Ilya Sherman, 2014/03/10 22:21:54]

Have you verified that the forward slashes work on all platforms?  (Really, I'm
wondering about Windows.)

+                                        '/permission_message.h'),

[Ilya Sherman, 2014/03/10 22:21:54]

nit: Why does this string start with a slash?

+                      start_marker='^enum ID {',
+                      end_marker='^kEnumBoundary',
+                      labelTransformer=StyleLabel)