VCM: Adding API for the size(duration) of the jitter buffer.

Refers to the duration in time of the frames which are ready to be sent to the decoder.

Review URL: https://webrtc-codereview.appspot.com/1319004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3903 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/main/source/jitter_buffer.h

@@ -166,6 +166,9 @@ class VCMJitterBuffer {
   int64_t LastDecodedTimestamp() const;
   bool decode_with_errors() const {return decode_with_errors_;}
 
+  // Returns size in time (milliseconds) of complete continuous frames.
+  int RenderBufferSizeMs();
+
  private:
   class SequenceNumberLessThan {
    public:
@@ -211,6 +214,8 @@ class VCMJitterBuffer {
   // Can return a decodable, incomplete frame when enabled.
   FrameList::iterator FindOldestCompleteContinuousFrame();
 
+  // Cleans the frame list in the JB from old/empty frames.
+  // Should only be called prior to actual use.
   void CleanUpOldOrEmptyFrames();
 
   // Sets the "decodable" and "frame loss" flags of a frame depending on which