Enable -Winconsistent-missing-override flag.

webrtc/modules/rtp_rtcp/source/rtcp_packet/receiver_report.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.
  */
 
@@ skipping 32 matching lines @@
  protected:
   bool Create(uint8_t* packet,
               size_t* index,
               size_t max_length,
               RtcpPacket::PacketReadyCallback* callback) const override;
 
  private:
   static const size_t kRrBaseLength = 4;
   static const size_t kMaxNumberOfReportBlocks = 0x1F;
 
-  size_t BlockLength() const {
+  size_t BlockLength() const override {
     return kHeaderLength + kRrBaseLength +
            report_blocks_.size() * ReportBlock::kLength;
   }
 
   uint32_t sender_ssrc_;
   std::vector<ReportBlock> report_blocks_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ReceiverReport);
 };
 
 }  // namespace rtcp
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_RECEIVER_REPORT_H_