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

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc

 /*
  *  Copyright (c) 2013 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 79 matching lines @@
   ModuleRtpRtcpImpl* receiver_;
   SimulatedClock* clock_;
   int64_t delay_ms_;
   int rtp_packets_sent_;
   RTPHeader last_rtp_header_;
   std::vector<uint16_t> last_nack_list_;
 };
 
 class RtpRtcpModule : public RtcpPacketTypeCounterObserver {
  public:
-  RtpRtcpModule(SimulatedClock* clock)
+  explicit RtpRtcpModule(SimulatedClock* clock)
       : receive_statistics_(ReceiveStatistics::Create(clock)) {
     RtpRtcp::Configuration config;
     config.audio = false;
     config.clock = clock;
     config.outgoing_transport = &transport_;
     config.receive_statistics = receive_statistics_.get();
     config.rtcp_packet_type_counter_observer = this;
     config.rtt_stats = &rtt_stats_;
 
     impl_.reset(new ModuleRtpRtcpImpl(config));
@@ skipping 429 matching lines @@
   EXPECT_EQ(6U, receiver_.RtcpSent().unique_nack_requests);
   EXPECT_THAT(receiver_.LastNackListSent(), ElementsAre(11, 18, 20, 21));
 
   // Send module receives the request.
   EXPECT_EQ(2U, sender_.RtcpReceived().nack_packets);
   EXPECT_EQ(8U, sender_.RtcpReceived().nack_requests);
   EXPECT_EQ(6U, sender_.RtcpReceived().unique_nack_requests);
   EXPECT_EQ(75, sender_.RtcpReceived().UniqueNackRequestsInPercent());
 }
 }  // namespace webrtc