Fix Chromium clang plugin warnings

NOTRY=true
BUG=webrtc:163

Review-Url: https://codereview.webrtc.org/2291503002
Cr-Commit-Position: refs/heads/master@{#13959}
diff --git a/webrtc/modules/audio_coding/test/Channel.h b/webrtc/modules/audio_coding/test/Channel.h
index 5910fad..c45864a 100644
--- a/webrtc/modules/audio_coding/test/Channel.h
+++ b/webrtc/modules/audio_coding/test/Channel.h
@@ -47,7 +47,7 @@
  public:
 
   Channel(int16_t chID = -1);
-  ~Channel();
+  ~Channel() override;
 
   int32_t SendData(FrameType frameType,
                    uint8_t payloadType,