Fix chromium-style warnings.

webrtc/modules/rtp_rtcp/source/rtp_rtcp_defines_nullimpl.cc

+/*
+ *  Copyright (c) 2016 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 "webrtc/modules/rtp_rtcp/source/rtp_rtcp_defines_nullimpl.h"
+
+namespace webrtc {
+
+int32_t NullRtpFeedback::OnInitializeDecoder(
+    int8_t payload_type,
+    const char payloadName[RTP_PAYLOAD_NAME_SIZE],
+    int frequency,
+    size_t channels,
+    uint32_t rate) {
+  return 0;
+}
+
+int32_t NullRtpData::OnReceivedPayloadData(const uint8_t* payload_data,
+                                           size_t payload_size,
+                                           const WebRtcRTPHeader* rtp_header) {
+  return 0;
+}
+
+bool NullRtpData::OnRecoveredPacket(const uint8_t* packet,
+                                    size_t packet_length) {
+  return true;
+}
+
+}  // namespace webrtc