Add nag_timer.

tests/subprocess2_test.py

Index: tests/subprocess2_test.py
diff --git a/tests/subprocess2_test.py b/tests/subprocess2_test.py
index 9d7df5bed2f715e22e7ba77e11911e93785acc2d..baeff6cab4ae90037e318f2c796537e8cbdb308a 100755
--- a/tests/subprocess2_test.py
+++ b/tests/subprocess2_test.py
@@ -591,7 +591,27 @@ class S2Test(BaseTestCase):
     except Blow:
       self.assertNotEquals(0, proc.returncode)
 
+  def test_nag_timer(self):
+    w = []
+    l = logging.getLogger()
+    class _Filter(logging.Filter):
+      def filter(self, record):
+        if record.levelno == logging.WARNING:
+          w.append(record.getMessage().lstrip())
+        return 0
+    f = _Filter()
+    l.addFilter(f)
+    proc = subprocess2.Popen(
+        self.exe + ['--stdout', '--sleep_first'], stdout=PIPE)
+    res = proc.communicate(nag_timer=3), proc.returncode
+    l.removeFilter(f)
+    self._check_res(res, 'A\nBB\nCCC\n', None, 0)
+    expected = ['No output for 3 seconds from command:', proc.cmd_str,
+                'No output for 6 seconds from command:', proc.cmd_str,
+                'No output for 9 seconds from command:', proc.cmd_str]
+    self.assertEquals(w, expected)
 
+    
 def child_main(args):
   if sys.platform == 'win32':
     # Annoying, make sure the output is not translated on Windows.