Fixes two bugs related to padding in the jitter buffer.

- Pad packets (empty) were often NACKed even though they were received.
- Padding only frames (empty) were didn't properly update the decoding state,
  and would therefore be NACKed even though they were received.

TEST=trybots

BUG=1150

Review URL: https://webrtc-codereview.appspot.com/929031

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3183 4adac7df-926f-26a2-2b94-8c16560cd09d

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

@@ -933,8 +933,7 @@ uint16_t* VCMJitterBuffer::CreateNackList(uint16_t* nack_list_size,
     // We don't need to check if frame is decoding since low_seq_num is based
     // on the last decoded sequence number.
     VCMFrameBufferStateEnum state = frame_buffers_[i]->GetState();
-    if ((kStateFree != state) &&
-        (kStateEmpty != state)) {
+    if (kStateFree != state) {
       // Reaching thus far means we are going to update the NACK list
       // When in hybrid mode, we use the soft NACKing feature.
       if (nack_mode_ == kNackHybrid) {
@@ -1271,11 +1270,11 @@ FrameList::iterator VCMJitterBuffer::FindOldestCompleteContinuousFrame(
 void VCMJitterBuffer::CleanUpOldFrames() {
   while (frame_list_.size() > 0) {
     VCMFrameBuffer* oldest_frame = frame_list_.front();
-    bool next_frame_empty =
-        (last_decoded_state_.ContinuousFrame(oldest_frame) &&
-         oldest_frame->GetState() == kStateEmpty);
-    if (last_decoded_state_.IsOldFrame(oldest_frame) ||
-        (next_frame_empty && frame_list_.size() > 1)) {
+    if (oldest_frame->GetState() == kStateEmpty && frame_list_.size() > 1) {
+      // This frame is empty, mark it as decoded, thereby making it old.
+      last_decoded_state_.UpdateEmptyFrame(oldest_frame);
+    }
+    if (last_decoded_state_.IsOldFrame(oldest_frame)) {
       ReleaseFrameIfNotDecoding(frame_list_.front());
       frame_list_.erase(frame_list_.begin());
     } else {