Remove unused thread.h include in trace_event_impl.h and fix IWUU.

ipc/ipc_send_fds_test.cc

 // Copyright (c) 2012 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 "build/build_config.h"
 
 #if defined(OS_POSIX)
 #if defined(OS_MACOSX)
 extern "C" {
 #include <sandbox.h>
 };
 #endif
 #include <fcntl.h>
 #include <stddef.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
 #include <memory>
 #include <queue>
 
 #include "base/callback.h"
 #include "base/file_descriptor_posix.h"
 #include "base/location.h"
 #include "base/pickle.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "ipc/ipc_message_attachment_set.h"
 #include "ipc/ipc_message_utils.h"
 #include "ipc/ipc_test_base.h"
 
 #if defined(OS_POSIX)
 #include "base/macros.h"
 #endif
 
 #if defined(OS_MACOSX)
@@ skipping 347 matching lines @@
   base::WaitableEvent received_;
 };
 
 TEST_F(IPCMultiSendingFdsTest, StressTest) {
   Run();
 }
 
 }  // namespace
 
 #endif  // defined(OS_POSIX)