Add some virtual and OVERRIDEs in webrtc/modules/audio_coding/

BUG=163
TBR=turaj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1900004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4447 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/audio_coding/neteq4/decoder_database.h b/webrtc/modules/audio_coding/neteq4/decoder_database.h
index 203e502..9effd52 100644
--- a/webrtc/modules/audio_coding/neteq4/decoder_database.h
+++ b/webrtc/modules/audio_coding/neteq4/decoder_database.h
@@ -65,18 +65,15 @@
   // only 7 bits).
   static const uint8_t kRtpPayloadTypeError = 0xFF;
 
-  DecoderDatabase()
-      : active_decoder_(-1),
-        active_cng_decoder_(-1) {
-  }
+  DecoderDatabase();
 
-  virtual ~DecoderDatabase() {}
+  virtual ~DecoderDatabase();
 
   // Returns true if the database is empty.
-  virtual bool Empty() const { return decoders_.empty(); }
+  virtual bool Empty() const;
 
   // Returns the number of decoders registered in the database.
-  virtual int Size() const { return decoders_.size(); }
+  virtual int Size() const;
 
   // Resets the database, erasing all registered payload types, and deleting
   // any AudioDecoder objects that were not externally created and inserted