[rtp_rtcp] fixed lint errors in rtp_rtcp module that are not fixed in other CLs

webrtc/modules/rtp_rtcp/source/rtp_header_extension.h

 /*
  *  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.
  */
 
@@ skipping 10 matching lines @@
 const uint16_t kRtpOneByteHeaderExtensionId = 0xBEDE;
 
 const size_t kRtpOneByteHeaderLength = 4;
 const size_t kTransmissionTimeOffsetLength = 4;
 const size_t kAudioLevelLength = 2;
 const size_t kAbsoluteSendTimeLength = 4;
 const size_t kVideoRotationLength = 2;
 const size_t kTransportSequenceNumberLength = 3;
 
 struct HeaderExtension {
-  HeaderExtension(RTPExtensionType extension_type)
+  explicit HeaderExtension(RTPExtensionType extension_type)
       : type(extension_type), length(0), active(true) {
     Init();
   }
 
   HeaderExtension(RTPExtensionType extension_type, bool active)
       : type(extension_type), length(0), active(active) {
     Init();
   }
 
   void Init() {
@@ skipping 67 matching lines @@
   RTPExtensionType Next(RTPExtensionType type) const;
 
  private:
   int32_t Register(const RTPExtensionType type, const uint8_t id, bool active);
   std::map<uint8_t, HeaderExtension*> extensionMap_;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTP_HEADER_EXTENSION_H_