Instantiate ScopedTaskEnvironment in net unittests.

net/dns/address_sorter_unittest.cc

Index: net/dns/address_sorter_unittest.cc
diff --git a/net/dns/address_sorter_unittest.cc b/net/dns/address_sorter_unittest.cc
index b9069df0c80e16eae98b9cdb7e04e0365d8da7d2..6c023997a33404bf905237837672e2ab83a9d049 100644
--- a/net/dns/address_sorter_unittest.cc
+++ b/net/dns/address_sorter_unittest.cc
@@ -10,8 +10,6 @@
 
 #include "base/bind.h"
 #include "base/logging.h"
-#include "base/message_loop/message_loop.h"
-#include "base/test/scoped_task_scheduler.h"
 #include "net/base/address_list.h"
 #include "net/base/ip_address.h"
 #include "net/base/test_completion_callback.h"
@@ -40,8 +38,6 @@ void OnSortComplete(AddressList* result_buf,
 }
 
 TEST(AddressSorterTest, Sort) {
-  base::test::ScopedTaskScheduler scoped_task_scheduler(
-      base::MessageLoop::current());
   int expected_result = OK;
 #if defined(OS_WIN)
   EnsureWinsockInit();