Ensure one does not register same rtp header extension with different id

webrtc/modules/rtp_rtcp/source/rtp_header_extension.cc

 /*
  *  Copyright (c) 2012 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.
  */
 
 #include <assert.h>
 
+#include "webrtc/base/checks.h"
 #include "webrtc/common_types.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_header_extension.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
 
 namespace webrtc {
 
+constexpr uint8_t RtpHeaderExtensionMap::kInvalidId;
+
 RtpHeaderExtensionMap::RtpHeaderExtensionMap() {
 }
 
 RtpHeaderExtensionMap::~RtpHeaderExtensionMap() {
   Erase();
 }
 
 void RtpHeaderExtensionMap::Erase() {
   while (!extensionMap_.empty()) {
     std::map<uint8_t, HeaderExtension*>::iterator it =
@@ skipping 12 matching lines @@
   if (it != extensionMap_.end()) {
     if (it->second->type != type) {
       // An extension is already registered with the same id
       // but a different type, so return failure.
       return -1;
     }
     // This extension type is already registered with this id,
     // so return success.
     return 0;
   }
+  RTC_DCHECK_EQ(kInvalidId, GetId(type));
   extensionMap_[id] = new HeaderExtension(type);
   return 0;
 }
 
 int32_t RtpHeaderExtensionMap::Deregister(const RTPExtensionType type) {
   uint8_t id;
   if (GetId(type, &id) != 0) {
     return 0;
   }
   std::map<uint8_t, HeaderExtension*>::iterator it =
@@ skipping 81 matching lines @@
   assert(map);
   std::map<uint8_t, HeaderExtension*>::const_iterator it =
       extensionMap_.begin();
   while (it != extensionMap_.end()) {
     HeaderExtension* extension = it->second;
     map->Register(extension->type, it->first);
     it++;
   }
 }
 }  // namespace webrtc