Wait for the make_expectations.py process to finish before checking return code.

BUG=None
TEST=perf_expectations_unittest.py should succeed if no expectations are waiting for updates.
TBR=cmp@chromium.org

Review URL: http://codereview.chromium.org/8318022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@105870 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf_expectations/tests/perf_expectations_unittest.py

@@ -150,6 +150,7 @@ class PerfExpectationsUnittest(unittest.TestCase):
 
   def testNoUpdatesNeeded(self):
     p = subprocess.Popen([MAKE_EXPECTATIONS, '-s'], stdout=subprocess.PIPE)
+    p.wait();
     self.assertEqual(p.returncode, 0, msg='Expectations has pending updates!')
 
   def testConfigFile(self):