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

components/leveldb/leveldb_mojo_proxy.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 "components/leveldb/leveldb_mojo_proxy.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/single_thread_task_runner.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/system/platform_handle.h"
 
 namespace leveldb {
 
 struct LevelDBMojoProxy::OpaqueLock {
   filesystem::mojom::FilePtr lock_file;
 };
 
 struct LevelDBMojoProxy::OpaqueDir {
@@ skipping 301 matching lines @@
     *out_lock = l;
   }
 }
 
 void LevelDBMojoProxy::UnlockFileImpl(std::unique_ptr<OpaqueLock> lock,
                                       filesystem::mojom::FileError* out_error) {
   lock->lock_file->Unlock(out_error);
 }
 
 }  // namespace leveldb