Fix clang style warnings in webrtc/modules/audio_coding/neteq

Mostly this consists of marking functions with override when
applicable, and moving function bodies from .h to .cc files.

BUG=163
R=henrik.lundin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44109004

Cr-Commit-Position: refs/heads/master@{#8960}
diff --git a/webrtc/modules/audio_coding/neteq/packet_buffer.cc b/webrtc/modules/audio_coding/neteq/packet_buffer.cc
index b0c939b..08b237f 100644
--- a/webrtc/modules/audio_coding/neteq/packet_buffer.cc
+++ b/webrtc/modules/audio_coding/neteq/packet_buffer.cc
@@ -49,6 +49,10 @@
   DeleteAllPackets(&buffer_);
 }
 
+bool PacketBuffer::Empty() const {
+  return buffer_.empty();
+}
+
 int PacketBuffer::InsertPacket(Packet* packet) {
   if (!packet || !packet->payload) {
     if (packet) {
@@ -229,6 +233,14 @@
   return 0;
 }
 
+int PacketBuffer::DiscardAllOldPackets(uint32_t timestamp_limit) {
+  return DiscardOldPackets(timestamp_limit, 0);
+}
+
+int PacketBuffer::NumPacketsInBuffer() const {
+  return static_cast<int>(buffer_.size());
+}
+
 int PacketBuffer::NumSamplesInBuffer(DecoderDatabase* decoder_database,
                                      int last_decoded_length) const {
   PacketList::const_iterator it;