Instantiate ScopedTaskEnvironment in net unittests.

net/test/net_test_suite.cc

Index: net/test/net_test_suite.cc
diff --git a/net/test/net_test_suite.cc b/net/test/net_test_suite.cc
index ff466e6e82bea025d4c81d725e1d74eb6a458818..2c6be66d13e510519f87b2e1274b045be5f49eb4 100644
--- a/net/test/net_test_suite.cc
+++ b/net/test/net_test_suite.cc
@@ -4,7 +4,8 @@
 
 #include "net/test/net_test_suite.h"
 
-#include "base/message_loop/message_loop.h"
+#include "base/memory/ptr_util.h"
+#include "base/test/scoped_task_environment.h"
 #include "net/base/network_change_notifier.h"
 #include "net/http/http_stream_factory.h"
 #include "net/spdy/chromium/spdy_session.h"
@@ -32,7 +33,7 @@ void NetTestSuite::Shutdown() {
 
   // We want to destroy this here before the TestSuite continues to tear down
   // the environment.
-  message_loop_.reset();
+  scoped_task_environment_.reset();
 
   TestSuite::Shutdown();
 }
@@ -51,5 +52,7 @@ void NetTestSuite::InitializeTestThreadNoNetworkChangeNotifier() {
   // the process of running these unit tests.
   host_resolver_proc_->AddRule("*", "127.0.0.1");
 
-  message_loop_.reset(new base::MessageLoopForIO());
+  scoped_task_environment_ =
+      base::MakeUnique<base::test::ScopedTaskEnvironment>(
+          base::test::ScopedTaskEnvironment::MainThreadType::IO);
 }