Replace const -> constexpr for rtcp Packet Type

webrtc/modules/rtp_rtcp/source/rtcp_packet/pli.h

 /*
  *  Copyright (c) 2015 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_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_PLI_H_
 #define WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_PLI_H_
 
 #include "webrtc/base/basictypes.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/psfb.h"
 
 namespace webrtc {
 namespace rtcp {
 class CommonHeader;
 // Picture loss indication (PLI) (RFC 4585).
 class Pli : public Psfb {
  public:
-  static const uint8_t kFeedbackMessageType = 1;
+  static constexpr uint8_t kFeedbackMessageType = 1;
 
   Pli() {}
   ~Pli() override {}
 
   bool Parse(const CommonHeader& packet);
 
  protected:
   bool Create(uint8_t* packet,
               size_t* index,
               size_t max_length,
               RtcpPacket::PacketReadyCallback* callback) const override;
 
  private:
   size_t BlockLength() const override {
     return kHeaderLength + kCommonFeedbackLength;
   }
 
   RTC_DISALLOW_COPY_AND_ASSIGN(Pli);
 };
 
 }  // namespace rtcp
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_PLI_H_