presubmit_unittest: Mock time_time for ThreadPoolTest

Mock time_time so that time.time is not called from ThreadPoolTest tests,
so that the execution time doesn't change between executions.

Bug: 1047631
Change-Id: I4f4ac30ca6a2ee3be25830c0e17a9f29a9c0c999
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2036477Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

tests/presubmit_unittest.py

@@ -3033,6 +3033,7 @@ class ThreadPoolTest(unittest.TestCase):
     super(ThreadPoolTest, self).setUp()
     mock.patch('subprocess2.Popen').start()
     mock.patch('presubmit_support.sigint_handler').start()
+    mock.patch('presubmit_support.time_time', return_value=0).start()
     presubmit.sigint_handler.wait.return_value = ('stdout', '')
     self.addCleanup(mock.patch.stopall)