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/decoding_state.cc

@@ -94,6 +94,13 @@ void VCMDecodingState::SetStateOneBack(const VCMFrameBuffer* frame) {
   init_ = false;
 }
 
+void VCMDecodingState::UpdateEmptyFrame(const VCMFrameBuffer* frame) {
+  if (ContinuousFrame(frame) && frame->GetState() == kStateEmpty) {
+    time_stamp_ = frame->TimeStamp();
+    sequence_num_ = frame->GetHighSeqNum();
+  }
+}
+
 void VCMDecodingState::UpdateOldPacket(const VCMPacket* packet) {
   assert(packet != NULL);
   if (packet->timestamp == time_stamp_) {