Reland of "Move RtcEventLog object from inside VoiceEngine to Call.", "Fix to make the start/stop f…

webrtc/call/rtc_event_log.h

Index: webrtc/call/rtc_event_log.h
diff --git a/webrtc/call/rtc_event_log.h b/webrtc/call/rtc_event_log.h
index bea57b01cd11eb4729b83f1967cb6258862ac7c2..7c72dd5ce995a4443a25af429154c4ce7f651bab 100644
--- a/webrtc/call/rtc_event_log.h
+++ b/webrtc/call/rtc_event_log.h
@@ -40,6 +40,9 @@ class RtcEventLog {
   // Factory method to create an RtcEventLog object.
   static std::unique_ptr<RtcEventLog> Create(const Clock* clock);
 
+  // Create an RtcEventLog object that does nothing.
+  static std::unique_ptr<RtcEventLog> CreateNull();
+
   // Starts logging a maximum of max_size_bytes bytes to the specified file.
   // If the file already exists it will be overwritten.
   // If max_size_bytes <= 0, logging will be active until StopLogging is called.