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/merge.h

@@ -33,17 +33,10 @@ class SyncBuffer;
 // what the Merge class does.
 class Merge {
  public:
-  Merge(int fs_hz, size_t num_channels, Expand* expand, SyncBuffer* sync_buffer)
-      : fs_hz_(fs_hz),
-        num_channels_(num_channels),
-        fs_mult_(fs_hz_ / 8000),
-        timestamps_per_call_(fs_hz_ / 100),
-        expand_(expand),
-        sync_buffer_(sync_buffer),
-        expanded_(num_channels_) {
-    assert(num_channels_ > 0);
-  }
-
+  Merge(int fs_hz,
+        size_t num_channels,
+        Expand* expand,
+        SyncBuffer* sync_buffer);
   virtual ~Merge() {}
 
   // The main method to produce the audio data. The decoded data is supplied in