Add presubmit scripts to check histograms.xml if bad_message.h changes.

tools/metrics/histograms/presubmit_bad_message_reasons.py

Index: tools/metrics/histograms/presubmit_bad_message_reasons.py
diff --git a/tools/metrics/histograms/presubmit_bad_message_reasons.py b/tools/metrics/histograms/presubmit_bad_message_reasons.py
new file mode 100644
index 0000000000000000000000000000000000000000..ef8842390621977e9d85da0ef11eb8fe7adac0ce
--- /dev/null
+++ b/tools/metrics/histograms/presubmit_bad_message_reasons.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.
+
+"""Check to see if the various BadMessage enums in histograms.xml need to be
+updated. This can be called from a chromium PRESUBMIT.py to ensure updates to
+bad_messages.h also include the generated changes to histograms.xml

[Ilya Sherman, 2017/01/27 23:35:13]

nit: bad_messages or bad_message, as typed below?

[dougt, 2017/01/28 00:58:11]

Done.

+"""
+
+import update_histogram_enum
+
+def PrecheckBadMessage(input_api, output_api, histogram_name):
+  source_path = ''
+
+  for f in input_api.AffectedFiles():
+    if f.LocalPath().endswith('bad_message.h'):

[dgozman, 2017/01/27 23:19:32]

Let's pass this as a parameter.

[dougt, 2017/01/27 23:25:47]

Acknowledged. It's always bad_message.h at this point, and this precheck is
about "bad message".

+      source_path = f.LocalPath()
+      break

[Ilya Sherman, 2017/01/27 23:35:13]

There are multiple bad_message files in the repository, right?  What if multiple
are changed in a single CL?  Will this break stmt mean that only the first one
is ever considered?

[dougt, 2017/01/28 00:58:11]

You will get one warning that asks you to run 'python
tools/metrics/histograms/update_bad_message_reasons.py'. Doing this will update
the histogram with the content from all bad_message.h files in the repo.

[Ilya Sherman, 2017/01/28 02:53:35]

Why are you guaranteed to get this warning?  It looks like the warning is only
emitted if the check below fails.  But, if only one of the bad_message.h files
is checked, then couldn't the warning be missed entirely?  (Perhaps I'm
misunderstanding something about how this all works?)

+
+  # If bad message wasn't change, then there is nothing to check.

[Ilya Sherman, 2017/01/27 23:35:13]

nit: s/bad message/bad_message.h

[Ilya Sherman, 2017/01/27 23:35:13]

nit: s/change/changed

[dougt, 2017/01/28 00:58:11]

Done.

+  if source_path == '':
+    return []
+
+  START_MARKER='^enum (class )?BadMessageReason {'
+  END_MARKER='^BAD_MESSAGE_MAX'
+  if update_histogram_enum.HistogramNeedsUpdate(
+      histogram_enum_name=histogram_name,
+      source_enum_path=source_path,
+      start_marker=START_MARKER,
+      end_marker=END_MARKER):
+    return [output_api.PresubmitPromptWarning(
+      'bad_messages.h has been updated but histogram.xml does not '
+      'appear to be updated.\nPlease run:\n'
+      '  python tools/metrics/histograms/update_bad_message_reasons.py\n')]
+  return []