Reland of Loosening the coupling between WebRTC and //third_party/protobuf

webrtc/logging/rtc_event_log/rtc_event_log_helper_thread.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_
 #define WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_
 
 #include <limits>
 #include <memory>
-#include <string>
 #include <utility>
 #include <vector>
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/event.h"
 #include "webrtc/base/ignore_wundef.h"
 #include "webrtc/base/platform_thread.h"
+#include "webrtc/base/protobuf_utils.h"
 #include "webrtc/base/swap_queue.h"
 #include "webrtc/logging/rtc_event_log/ringbuffer.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 
 #ifdef ENABLE_RTC_EVENT_LOG
-// Files generated at build-time by the protobuf compiler.
+// *.ph.h files are generated at build-time by the protobuf compiler.
 RTC_PUSH_IGNORING_WUNDEF()
 #ifdef WEBRTC_ANDROID_PLATFORM_BUILD
 #include "external/webrtc/webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
 #else
 #include "webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
 #endif
 RTC_POP_IGNORING_WUNDEF()
 #endif
 
 #ifdef ENABLE_RTC_EVENT_LOG
@@ skipping 65 matching lines @@
 
   int64_t max_size_bytes_;
   int64_t written_bytes_;
   int64_t start_time_;
   int64_t stop_time_;
 
   bool has_recent_event_;
   std::unique_ptr<rtclog::Event> most_recent_event_;
 
   // Temporary space for serializing profobuf data.
-  std::string output_string_;
+  ProtoString output_string_;
 
   rtc::Event wake_periodically_;
   rtc::Event wake_from_hibernation_;
   rtc::Event file_finished_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(RtcEventLogHelperThread);
 };
 
 }  // namespace webrtc
 
 #endif  // ENABLE_RTC_EVENT_LOG
 
 #endif  // WEBRTC_LOGGING_RTC_EVENT_LOG_RTC_EVENT_LOG_HELPER_THREAD_H_