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}

webrtc/modules/audio_coding/neteq/audio_vector.cc

@@ -18,6 +18,21 @@
 
 namespace webrtc {
 
+AudioVector::AudioVector()
+    : array_(new int16_t[kDefaultInitialSize]),
+      first_free_ix_(0),
+      capacity_(kDefaultInitialSize) {
+}
+
+AudioVector::AudioVector(size_t initial_size)
+    : array_(new int16_t[initial_size]),
+      first_free_ix_(initial_size),
+      capacity_(initial_size) {
+  memset(array_.get(), 0, initial_size * sizeof(int16_t));
+}
+
+AudioVector::~AudioVector() = default;
+
 void AudioVector::Clear() {
   first_free_ix_ = 0;
 }
@@ -145,6 +160,16 @@ void AudioVector::CrossFade(const AudioVector& append_this,
     PushBack(&append_this[fade_length], samples_to_push_back);
 }
 
+// Returns the number of elements in this AudioVector.
+size_t AudioVector::Size() const {
+  return first_free_ix_;
+}
+
+// Returns true if this AudioVector is empty.
+bool AudioVector::Empty() const {
+  return first_free_ix_ == 0;
+}
+
 const int16_t& AudioVector::operator[](size_t index) const {
   return array_[index];
 }