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diff --git a/third_party/libwebrtc/build/compute_build_timestamp.py b/third_party/libwebrtc/build/compute_build_timestamp.py
new file mode 100755
index 0000000000..ceb507b26c
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+++ b/third_party/libwebrtc/build/compute_build_timestamp.py
@@ -0,0 +1,126 @@
+#!/usr/bin/env python
+# Copyright 2018 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.
+"""Returns a timestamp that approximates the build date.
+
+build_type impacts the timestamp generated, both relative to the date of the
+last recent commit:
+- default: the build date is set to the most recent first Sunday of a month at
+  5:00am. The reason is that it is a time where invalidating the build cache
+  shouldn't have major repercussions (due to lower load).
+- official: the build date is set to the time of the most recent commit.
+Either way, it is guaranteed to be in the past and always in UTC.
+"""
+
+# The requirements for the timestamp:
+# (1) for the purposes of continuous integration, longer duration
+#     between cache invalidation is better, but >=1mo is preferable.
+# (2) for security purposes, timebombs would ideally be as close to
+#     the actual time of the build as possible. It must be in the past.
+# (3) HSTS certificate pinning is valid for 70 days. To make CI builds enforce
+#     HTST pinning, <=1mo is preferable.
+#
+# On Windows, the timestamp is also written in the PE/COFF file header of
+# executables of dlls.  That timestamp and the executable's file size are
+# the only two pieces of information that identify a given executable on
+# the symbol server, so rarely changing timestamps can cause conflicts there
+# as well. We only upload symbols for official builds to the symbol server.
+
+from __future__ import print_function
+
+import argparse
+import calendar
+import datetime
+import doctest
+import os
+import sys
+
+
+THIS_DIR = os.path.abspath(os.path.dirname(__file__))
+
+
+def GetFirstSundayOfMonth(year, month):
+  """Returns the first sunday of the given month of the given year.
+
+  >>> GetFirstSundayOfMonth(2016, 2)
+  7
+  >>> GetFirstSundayOfMonth(2016, 3)
+  6
+  >>> GetFirstSundayOfMonth(2000, 1)
+  2
+  """
+  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 GetUnofficialBuildDate(build_date):
+  """Gets the approximate build date given the specific build type.
+
+  >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 6, 1, 2, 3))
+  datetime.datetime(2016, 1, 3, 5, 0)
+  >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 7, 5))
+  datetime.datetime(2016, 2, 7, 5, 0)
+  >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 8, 5))
+  datetime.datetime(2016, 2, 7, 5, 0)
+  """
+
+  if build_date.hour < 5:
+    # The time is locked at 5:00 am in UTC to cause the build cache
+    # invalidation to not happen exactly at midnight. Use the same calculation
+    # as the day before.
+    # See //base/build_time.cc.
+    build_date = build_date - datetime.timedelta(days=1)
+  build_date = datetime.datetime(build_date.year, build_date.month,
+                                 build_date.day, 5, 0, 0)
+
+  day = build_date.day
+  month = build_date.month
+  year = build_date.year
+  first_sunday = GetFirstSundayOfMonth(year, month)
+  # 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(year, month)
+  return datetime.datetime(
+      year, month, day, build_date.hour, build_date.minute, build_date.second)
+
+
+def main():
+  if doctest.testmod()[0]:
+    return 1
+  argument_parser = argparse.ArgumentParser()
+  argument_parser.add_argument(
+      'build_type', help='The type of build', choices=('official', 'default'))
+  args = argument_parser.parse_args()
+
+  # The mtime of the revision in build/util/LASTCHANGE is stored in a file
+  # next to it. Read it, to get a deterministic time close to "now".
+  # That date is then modified as described at the top of the file so that
+  # it changes less frequently than with every commit.
+  # This intentionally always uses build/util/LASTCHANGE's commit time even if
+  # use_dummy_lastchange is set.
+  lastchange_file = os.path.join(THIS_DIR, 'util', 'LASTCHANGE.committime')
+  last_commit_timestamp = int(open(lastchange_file).read())
+  build_date = datetime.datetime.utcfromtimestamp(last_commit_timestamp)
+
+  # For official builds we want full fidelity time stamps because official
+  # builds are typically added to symbol servers and Windows symbol servers
+  # use the link timestamp as the prime differentiator, but for unofficial
+  # builds we do lots of quantization to avoid churn.
+  if args.build_type != 'official':
+    build_date = GetUnofficialBuildDate(build_date)
+  print(int(calendar.timegm(build_date.utctimetuple())))
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())