[Sync] Move the last things out of core/.

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 "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