Use ScopedTaskEnvironment instead of MessageLoop in chromeos unit tests.

ScopedTaskEnvironment allows usage of ThreadTaskRunnerHandle and
base/task_scheduler/post_task.h within its scope. It should be
instantiated in every unit test that uses either of these APIs
(i.e. no test should instantiate a MessageLoop directly).

Motivation for ScopedTaskEnvironment can be found in:
https://docs.google.com/document/d/1QabRo8c7D9LsYY3cEcaPQbOCLo8Tu-6VLykYXyl3Pkk/edit

BUG=708584
[email protected]
[email protected], [email protected], [email protected]

Review-Url: https://codereview.chromium.org/2799753002
Cr-Commit-Position: refs/heads/master@{#462486}
diff --git a/chromeos/network/network_connect_unittest.cc b/chromeos/network/network_connect_unittest.cc
index 90d2444..80689f2 100644
--- a/chromeos/network/network_connect_unittest.cc
+++ b/chromeos/network/network_connect_unittest.cc
@@ -9,6 +9,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/shill_device_client.h"
 #include "chromeos/dbus/shill_service_client.h"
@@ -146,7 +147,7 @@
 
   std::unique_ptr<MockDelegate> mock_delegate_;
   std::unique_ptr<MockTetherDelegate> mock_tether_delegate_;
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   ShillDeviceClient::TestInterface* device_test_;
   ShillServiceClient::TestInterface* service_test_;