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

ipc/attachment_broker_mac_unittest.cc

 // Copyright 2015 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"
 
 #include <fcntl.h>
 #include <mach/mach_vm.h>
 #include <stddef.h>
 #include <sys/mman.h>
 
 #include <memory>
 #include <tuple>
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/mach_logging.h"
 #include "base/memory/free_deleter.h"
 #include "base/memory/shared_memory.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/synchronization/spin_wait.h"
+#include "base/threading/thread.h"
 #include "base/time/time.h"
 #include "ipc/attachment_broker_messages.h"
 #include "ipc/attachment_broker_privileged_mac.h"
 #include "ipc/attachment_broker_unprivileged_mac.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_test_base.h"
 #include "ipc/ipc_test_messages.h"
 #include "ipc/test_util_mac.h"
 
@@ skipping 1254 matching lines @@
     SendControlMessage(sender, success);
   }
 }
 
 MULTIPROCESS_IPC_TEST_CLIENT_MAIN(MemoryUsageManyMessages) {
   return CommonPrivilegedProcessMain(&MemoryUsageManyMessagesCallback,
                                      "MemoryUsageManyMessages");
 }
 
 }  // namespace