Add missing IWYU message_loop.h includes.

ui/events/blink/input_handler_proxy_unittest.cc

 // Copyright 2013 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 "ui/events/blink/input_handler_proxy.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted_memory.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "base/test/trace_event_analyzer.h"
 #include "base/trace_event/trace_buffer.h"
 #include "cc/input/main_thread_scrolling_reason.h"
 #include "cc/trees/swap_promise_monitor.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 3845 matching lines @@
 INSTANTIATE_TEST_CASE_P(AnimateInput,
                         InputHandlerProxyWithoutWheelScrollLatchingTest,
                         testing::ValuesIn(test_types));
 
 INSTANTIATE_TEST_CASE_P(InputHandlerProxyEventQueueTests,
                         InputHandlerProxyEventQueueTest,
                         testing::Bool());
 
 }  // namespace test
 }  // namespace ui