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/interface/video_coding.h

@@ -412,6 +412,10 @@ public:
     //                     < 0,         on error.
     virtual int32_t Decode(uint16_t maxWaitTimeMs = 200) = 0;
 
+    // Registers a callback which conveys the size of the render buffer.
+    virtual int RegisterRenderBufferSizeCallback(
+        VCMRenderBufferSizeCallback* callback) = 0;
+
     // Waits for the next frame in the dual jitter buffer to become complete
     // (waits no longer than maxWaitTimeMs), then passes it to the dual decoder
     // for decoding. This will never trigger a render callback. Should be