Fix Chromium clang plugin warnings

This adds a new file, webrtc/modules/audio_coding/neteq/tools/packet_source.cc, so that I'll have somewhere to put the new non-inlined methods.

NOTRY=true
BUG=webrtc:163

Review-Url: https://codereview.webrtc.org/2290593002
Cr-Commit-Position: refs/heads/master@{#13956}
diff --git a/webrtc/modules/audio_coding/neteq/tools/packet.h b/webrtc/modules/audio_coding/neteq/tools/packet.h
index 86eedc0..d150805 100644
--- a/webrtc/modules/audio_coding/neteq/tools/packet.h
+++ b/webrtc/modules/audio_coding/neteq/tools/packet.h
@@ -62,7 +62,7 @@
          size_t virtual_packet_length_bytes,
          double time_ms);
 
-  virtual ~Packet() {}
+  virtual ~Packet();
 
   // Parses the first bytes of the RTP payload, interpreting them as RED headers
   // according to RFC 2198. The headers will be inserted into |headers|. The