Shutdown the It2Me host cleanly.

remoting/host/it2me/it2me_native_messaging_host_unittest.cc

Index: remoting/host/it2me/it2me_native_messaging_host_unittest.cc
diff --git a/remoting/host/it2me/it2me_native_messaging_host_unittest.cc b/remoting/host/it2me/it2me_native_messaging_host_unittest.cc
index d65583cfb52799a892c43dddfb1769c78495c43b..a3f4eb56de82c6697807630a529529817eefab4a 100644
--- a/remoting/host/it2me/it2me_native_messaging_host_unittest.cc
+++ b/remoting/host/it2me/it2me_native_messaging_host_unittest.cc
@@ -190,7 +190,6 @@ class It2MeNativeMessagingHostTest : public testing::Test {
 
  private:
   void StartHost();
-  void StopHost();
   void ExitTest();
 
   // Each test creates two unidirectional pipes: "input" and "output".
@@ -239,6 +238,10 @@ void It2MeNativeMessagingHostTest::SetUp() {
 }
 
 void It2MeNativeMessagingHostTest::TearDown() {
+  // Release reference to AutoThreadTaskRunner, so the host thread can be shut
+  // down.
+  host_task_runner_ = nullptr;
+
   // Closing the write-end of the input will send an EOF to the native
   // messaging reader. This will trigger a host shutdown.
   input_write_file_.Close();
@@ -443,28 +446,13 @@ void It2MeNativeMessagingHostTest::StartHost() {
           make_scoped_ptr(new MockIt2MeHostFactory())));
   it2me_host->Start(pipe_.get());
 
-  pipe_->Start(it2me_host.Pass(),
-               channel.Pass(),
-               base::Bind(&It2MeNativeMessagingHostTest::StopHost,
-                          base::Unretained(this)));
+  pipe_->Start(it2me_host.Pass(), channel.Pass());
 
   // Notify the test that the host has finished starting up.
   test_message_loop_->message_loop_proxy()->PostTask(
       FROM_HERE, test_run_loop_->QuitClosure());
 }
 
-void It2MeNativeMessagingHostTest::StopHost() {
-  DCHECK(host_task_runner_->RunsTasksOnCurrentThread());
-
-  pipe_.reset();
-
-  // Wait till all shutdown tasks have completed.
-  base::RunLoop().RunUntilIdle();
-
-  // Trigger a test shutdown via ExitTest().
-  host_task_runner_ = nullptr;
-}
-
 void It2MeNativeMessagingHostTest::ExitTest() {
   if (!test_message_loop_->message_loop_proxy()->RunsTasksOnCurrentThread()) {
     test_message_loop_->message_loop_proxy()->PostTask(