Reland of Make rtcp parsing implementation private in RtcpReceiver (patchset #1 id:1 of https://codereview.webrtc.org/2332673003/ )

Reason for revert:
Fuzzer changed not use functions moved to private.

Original issue's description:
> Revert of Make rtcp parsing implementation private in RtcpReceiver (patchset #1 id:1 of https://codereview.webrtc.org/2320603002/ )
>
> Reason for revert:
> Breaks fuzzer compilation.
>
> Original issue's description:
> > Make rtcp parsing implementation private in RtcpReceiver:
> > Function just for Parse and for Callbacks moved to private section.
> > All handles moved from protected to private section.
> >
> > BUG=webrtc:5260
> > R=sprang@webrtc.org
> >
> > Committed: https://crrev.com/faf708e238c7b43a732fbebf79ac9298b4b95a95
> > Cr-Commit-Position: refs/heads/master@{#14181}
>
> TBR=sprang@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:5260
>
> Committed: https://crrev.com/180e4525ca7c9a23602cdf37a8756df7d23e7143
> Cr-Commit-Position: refs/heads/master@{#14182}

TBR=sprang@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:5260

Review-Url: https://codereview.webrtc.org/2336213002
Cr-Commit-Position: refs/heads/master@{#14200}
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h b/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
index 3659374..e9d2c94 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_receiver.h
@@ -60,13 +60,6 @@
   void SetRemoteSSRC(uint32_t ssrc);
   uint32_t RemoteSSRC() const;
 
-  int32_t IncomingRTCPPacket(
-      RTCPHelp::RTCPPacketInformation& rtcpPacketInformation,
-      RTCPUtility::RTCPParserV2* rtcpParser);
-
-  void TriggerCallbacksFromRTCPPacket(
-      RTCPHelp::RTCPPacketInformation& rtcpPacketInformation);
-
   // get received cname
   int32_t CNAME(uint32_t remoteSSRC, char cName[RTCP_CNAME_SIZE]) const;
 
@@ -115,7 +108,21 @@
   void RegisterRtcpStatisticsCallback(RtcpStatisticsCallback* callback);
   RtcpStatisticsCallback* GetRtcpStatisticsCallback();
 
- protected:
+ private:
+  using ReceivedInfoMap = std::map<uint32_t, RTCPHelp::RTCPReceiveInformation*>;
+  // RTCP report block information mapped by remote SSRC.
+  using ReportBlockInfoMap =
+      std::map<uint32_t, RTCPHelp::RTCPReportBlockInformation*>;
+  // RTCP report block information map mapped by source SSRC.
+  using ReportBlockMap = std::map<uint32_t, ReportBlockInfoMap>;
+
+  int32_t IncomingRTCPPacket(
+      RTCPHelp::RTCPPacketInformation& rtcpPacketInformation,
+      RTCPUtility::RTCPParserV2* rtcpParser);
+
+  void TriggerCallbacksFromRTCPPacket(
+      RTCPHelp::RTCPPacketInformation& rtcpPacketInformation);
+
   RTCPUtility::RTCPCnameInformation* CreateCnameInformation(
       uint32_t remoteSSRC);
   RTCPUtility::RTCPCnameInformation* GetCnameInformation(
@@ -253,14 +260,6 @@
       RTCPHelp::RTCPPacketInformation* rtcp_packet_information)
       EXCLUSIVE_LOCKS_REQUIRED(_criticalSectionRTCPReceiver);
 
- private:
-  typedef std::map<uint32_t, RTCPHelp::RTCPReceiveInformation*> ReceivedInfoMap;
-  // RTCP report block information mapped by remote SSRC.
-  typedef std::map<uint32_t, RTCPHelp::RTCPReportBlockInformation*>
-      ReportBlockInfoMap;
-  // RTCP report block information map mapped by source SSRC.
-  typedef std::map<uint32_t, ReportBlockInfoMap> ReportBlockMap;
-
   RTCPHelp::RTCPReportBlockInformation* CreateOrGetReportBlockInformation(
       uint32_t remote_ssrc,
       uint32_t source_ssrc)