Add missing IWYU message_loop.h includes.

device/geolocation/geolocation_provider_impl_unittest.cc

 // Copyright 2014 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 "device/geolocation/geolocation_provider_impl.h"
 
 #include <memory>
 
 #include "base/at_exit.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/location.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/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string16.h"
 #include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "device/geolocation/access_token_store.h"
 #include "device/geolocation/fake_location_provider.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 223 matching lines @@
       base::Bind(&MockGeolocationObserver::OnLocationUpdate,
                  base::Unretained(&mock_observer));
   std::unique_ptr<GeolocationProvider::Subscription> subscription =
       provider()->AddLocationUpdateCallback(callback, false);
   subscription.reset();
   // Wait for the providers to be stopped now that all clients are gone.
   EXPECT_FALSE(ProvidersStarted());
 }
 
 }  // namespace device