[Sync] Removing duplicated includes between cc and h files.

components/sync/core_impl/protocol_event_buffer.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 "components/sync/core_impl/protocol_event_buffer.h"
 
-#include <stddef.h>
-
 #include "components/sync/engine/events/protocol_event.h"
 
 namespace syncer {
 
 const size_t ProtocolEventBuffer::kBufferSize = 6;
 
 ProtocolEventBuffer::ProtocolEventBuffer() {}
 
 ProtocolEventBuffer::~ProtocolEventBuffer() {}
 
 void ProtocolEventBuffer::RecordProtocolEvent(const ProtocolEvent& event) {
   buffer_.push_back(event.Clone());
   if (buffer_.size() > kBufferSize)
     buffer_.pop_front();
 }
 
 std::vector<std::unique_ptr<ProtocolEvent>>
 ProtocolEventBuffer::GetBufferedProtocolEvents() const {
   std::vector<std::unique_ptr<ProtocolEvent>> ret;
   for (auto& event : buffer_)
     ret.push_back(event->Clone());
 
   return ret;
 }
 
 }  // namespace syncer