Makes GetBuildTime behave identically on all build types.

build/write_build_date_header.py

Index: build/write_build_date_header.py
diff --git a/build/write_build_date_header.py b/build/write_build_date_header.py
new file mode 100755
index 0000000000000000000000000000000000000000..6e10c829793d36481544a46d7dbe3af0766875b2
--- /dev/null
+++ b/build/write_build_date_header.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python
+# Copyright (c) 2016 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.
+"""Writes a file that contains a define that approximates the build date.
+
+The build date is set to the most recent first Sunday of a month, in UTC time.
+The reason for using the first Sunday of a month is that it is a time where
+invalidating the build cache shouldn't have major reprecussions.
+"""
+
+import argparse
+import calendar
+import datetime
+import os
+import sys
+
+
+def GetFirstSundayOfMonth(month, year):
+  """Returns the first sunday of the given month of the given year."""
+  weeks = calendar.Calendar().monthdays2calendar(year, month)
+  # Return the first day in the first week that is a Sunday.
+  return [date_day[0] for date_day in weeks[0] if date_day[1] == 6][0]
+
+
+def GetBuildDate(build_type):
+  """Gets the approximate build date given the specific build type."""
+  gmt_now = datetime.datetime.utcnow()
+  day = gmt_now.day
+  month = gmt_now.month
+  year = gmt_now.year
+  if build_type != 'official':
+    first_sunday = GetFirstSundayOfMonth(month, year)
+    # If our build is after the first Sunday, we've already refreshed our build
+    # cache on a quiet day, so just use that day.
+    # Otherwise, take the first Sunday of the previous month.
+    if day >= first_sunday:
+      day = first_sunday
+    else:
+      month -= 1
+      if month == 0:
+        month = 12
+        year -= 1
+      day = GetFirstSundayOfMonth(month, year)
+  return "{:%b %d %Y}".format(datetime.date(year, month, day))
+
+
+def main():
+  argument_parser = argparse.ArgumentParser()
+  argument_parser.add_argument('output_file', help='The file to write to')
+  argument_parser.add_argument('build_type', help='The type of build',
+                               choices=("official", "default"))
+  argument_parser.add_argument('build_date_override', nargs='?',
+                               help='Optional override for the build date')
+  args = argument_parser.parse_args()
+
+  if args.build_date_override:
+    build_date = args.build_date_override
+  else:
+    build_date = GetBuildDate(args.build_type)
+
+  output = ('// Generated by //build/write_build_date_header.py\n'
+           '#ifndef BUILD_DATE\n'
+           '#define BUILD_DATE "{}"\n'
+           '#endif // BUILD_DATE\n'.format(build_date))
+
+  current_contents = ""
+  if os.path.isfile(args.output_file):
+    with open(args.output_file, 'r') as current_file:
+      current_contents = current_file.read()
+
+  if current_contents != output:
+    with open(args.output_file, 'w') as output_file:
+      output_file.write(output)
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())