Instantiate ScopedTaskEnvironment in net unittests.

net/test/net_test_suite.h

Index: net/test/net_test_suite.h
diff --git a/net/test/net_test_suite.h b/net/test/net_test_suite.h
index 6b154a8e4fc1757fec912e83ce9d750dd9dc9646..b059bf2e8ba1a47327b0482261fdb0842d47cac4 100644
--- a/net/test/net_test_suite.h
+++ b/net/test/net_test_suite.h
@@ -13,7 +13,9 @@
 #include "net/dns/mock_host_resolver.h"
 
 namespace base {
-class MessageLoop;
+namespace test {
+class ScopedTaskEnvironment;
+}
 }
 
 namespace net {
@@ -44,7 +46,7 @@ class NetTestSuite : public base::TestSuite {
 
  private:
   std::unique_ptr<net::NetworkChangeNotifier> network_change_notifier_;
-  std::unique_ptr<base::MessageLoop> message_loop_;
+  std::unique_ptr<base::test::ScopedTaskEnvironment> scoped_task_environment_;
   scoped_refptr<net::RuleBasedHostResolverProc> host_resolver_proc_;
   net::ScopedDefaultHostResolverProc scoped_host_resolver_proc_;
 };