Kill any lingering spawning test server on Android when handling /start

build/android/pylib/chrome_test_server_spawner.py

 # Copyright 2013 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.
 
 """A "Test Server Spawner" that handles killing/stopping per-test test servers.
 
 It's used to accept requests from the device to spawn and kill instances of the
 chrome test server on the host.
 """
 # pylint: disable=W0702
@@ skipping 303 matching lines @@
     content_length = self.headers.getheader('content-length')
     if not content_length:
       content_length = 0
     try:
       content_length = int(content_length)
     except:
       raise Exception('Bad content-length for start request.')
     logging.info(content_length)
     test_server_argument_json = self.rfile.read(content_length)
     logging.info(test_server_argument_json)
-    assert not self.server.test_server_instance
+    # There should only be one test server instance at a time. However it may
+    # be possible that a previous instance was not cleaned up properly
+    # (crbug.com/665686)
+    if self.server.test_server_instance:
+      port = self.server.test_server_instance.host_port
+      logging.info('Killing lingering test server instance on port: %d', port)
+      self.server.test_server_instance.Stop()
+      self.server.test_server_instance = None
     ready_event = threading.Event()
     self.server.test_server_instance = TestServerThread(
         ready_event,
         json.loads(test_server_argument_json),
         self.server.device,
         self.server.tool)
     self.server.test_server_instance.setDaemon(True)
     self.server.test_server_instance.start()
     ready_event.wait()
     if self.server.test_server_instance.is_ready:
@@ skipping 88 matching lines @@
 
   def CleanupState(self):
     """Cleans up the spawning server state.
 
     This should be called if the test server spawner is reused,
     to avoid sharing the test server instance.
     """
     if self.server.test_server_instance:
       self.server.test_server_instance.Stop()
       self.server.test_server_instance = None