Adds two convenience functions for later use.

infra/libs/time_functions/test/timestamp_test.py

+# Copyright 2015 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.
+
+import datetime
+from pytz import timezone
+import unittest
+
+from infra.libs.time_functions import timestamp
+
+
+class TestTimestamps(unittest.TestCase):
+  def testTimestamp(self):
+    sec_diff = 1000
+    my_date = datetime.datetime.utcfromtimestamp(sec_diff)
+    self.assertEqual(timestamp.utctimestamp(my_date), sec_diff)

[tandrii(chromium), 2015/04/24 18:10:43]

wdyt about emphasizing floatness of utctimestamp return type by
s/sec_diff/float(sec_diff) 
?

[ghost stip (do not use), 2015/04/27 22:18:18]

I believe the check will work anyway (1.0 == 1), but I'll go ahead and make the
change

+
+  def testTimeZoneTimestamp(self):
+    sec_diff = 1000
+    my_date = datetime.datetime.utcfromtimestamp(sec_diff)
+    my_date = my_date.replace(tzinfo=timezone('Etc/GMT-8'))
+
+    pst_diff = sec_diff - (8 * 3600.0)

[tandrii(chromium), 2015/04/24 18:10:43]

well, this is implicitly float, but i'd still make it explicitely float on the
next line.

[ghost stip (do not use), 2015/04/27 22:18:18]

Done.

+    self.assertEqual(timestamp.utctimestamp(my_date), pst_diff)