Upgrade to coverage 3.7.1 and have it auto-build itself on first use.

scripts/slave/unittests/expect_tests/cover.py

 # Copyright 2014 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.
 
 from cStringIO import StringIO
 
-try:
-  import coverage
-  coverage_version = coverage.__version__
-except ImportError:
-  coverage = None
-  coverage_version = None
+import test_env  # pylint: disable=W0611
 
-from distutils.version import StrictVersion
-
-if (not coverage or
-    not hasattr(coverage.collector, 'CTracer') or
-    not coverage.collector.CTracer or
-    StrictVersion(coverage_version) < StrictVersion('3.7')):
-  raise ImportError(
-      'This test requires natively-installed python-coverage (>=3.7). '
-      'Current is %s.' % coverage_version)
-
+import coverage
 
 # This is instead of a contextmanager because it causes old pylints to crash :(
 class _Cover(object):
   def __init__(self, enabled, maybe_kwargs):
     self.enabled = enabled
     self.kwargs = maybe_kwargs or {}
     self.c = None
 
   def __enter__(self):
     if self.enabled:
@@ skipping 46 matching lines @@
         print
         print 'FATAL: Test coverage is not at 100%.'
 
     return not fail
 
   def create_subprocess_context(self):
     # Can't have this method be the contextmanager because otherwise
     # self (and self.cov) will get pickled to the subprocess, and we don't want
     # that :(
     return _Cover(self.enabled, self.opts)