Add missing IWYU message_loop.h includes.

components/grpc_support/test/get_stream_engine.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread.h"
 #include "components/grpc_support/include/bidirectional_stream_c.h"
 #include "components/grpc_support/test/quic_test_server.h"
 #include "net/base/host_port_pair.h"
 #include "net/cert/mock_cert_verifier.h"
 #include "net/dns/mapped_host_resolver.h"
 #include "net/dns/mock_host_resolver.h"
 #include "net/http/http_server_properties_impl.h"
@@ skipping 104 matching lines @@
   g_request_context_getter_.Get()->SetTestServerPort(port);
   static stream_engine engine;
   engine.obj = g_request_context_getter_.Get().get();
   return &engine;
 }
 
 void StartTestStreamEngine(int port) {}
 void ShutdownTestStreamEngine() {}
 
 }  // namespace grpc_support