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

webrtc/logging/rtc_event_log/rtc_event_log.cc

Index: webrtc/logging/rtc_event_log/rtc_event_log.cc
diff --git a/webrtc/logging/rtc_event_log/rtc_event_log.cc b/webrtc/logging/rtc_event_log/rtc_event_log.cc
index d10dc98232bcb95c3ab88ef9fb7acb9b2ff49272..68d213e5284a05693a733d7cb89dd49d53510c75 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log.cc
+++ b/webrtc/logging/rtc_event_log/rtc_event_log.cc
@@ -17,6 +17,7 @@
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/event.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/base/protobuf_utils.h"
 #include "webrtc/base/swap_queue.h"
 #include "webrtc/base/thread_checker.h"
 #include "webrtc/base/timeutils.h"
@@ -38,7 +39,7 @@
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 
 #ifdef ENABLE_RTC_EVENT_LOG
-// Files generated at build-time by the protobuf compiler.
+// *.pb.h files are generated at build-time by the protobuf compiler.
 #ifdef WEBRTC_ANDROID_PLATFORM_BUILD
 #include "external/webrtc/webrtc/logging/rtc_event_log/rtc_event_log.pb.h"
 #else
@@ -584,7 +585,7 @@ bool RtcEventLog::ParseRtcEventLog(const std::string& file_name,
   if (!dump_file->OpenFile(file_name.c_str(), true)) {
     return false;
   }
-  std::string dump_buffer;
+  ProtoString dump_buffer;
   while ((bytes_read = dump_file->Read(tmp_buffer, sizeof(tmp_buffer))) > 0) {
     dump_buffer.append(tmp_buffer, bytes_read);
   }