Use ScopedTaskEnvironment instead of MessageLoop in components unit tests.

components/nacl/loader/nacl_ipc_adapter_unittest.cc

Index: components/nacl/loader/nacl_ipc_adapter_unittest.cc
diff --git a/components/nacl/loader/nacl_ipc_adapter_unittest.cc b/components/nacl/loader/nacl_ipc_adapter_unittest.cc
index b89eb353dadaec8ef0ac92dd2e3610a82b3d6f04..9eaa4b011f12a73833717df2777fba1eba2d8540 100644
--- a/components/nacl/loader/nacl_ipc_adapter_unittest.cc
+++ b/components/nacl/loader/nacl_ipc_adapter_unittest.cc
@@ -11,6 +11,7 @@
 #include <memory>
 
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/simple_thread.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ -58,7 +59,7 @@ class NaClIPCAdapterTest : public testing::Test {
     return adapter_->Send(&msg);
   }
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
 
   scoped_refptr<NaClIPCAdapter> adapter_;