Refactor NACK list creation to build the NACK list as packets arrive.

Also fixes a timer bug related to NACKing in the RTP module which could cause packets to only be NACKed twice if there's frequent packet losses.

Note that I decided to remove any selective NACKing for now as I don't think the gain of doing it is big enough compared to the added complexity. The same reasoning for empty packets. None of them will be retransmitted by a smart sender since the sender would know that they aren't needed.

BUG=1420
TEST=video_coding_unittests, vie_auto_test, video_coding_integrationtests, trybots

Review URL: https://webrtc-codereview.appspot.com/1115006

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3599 4adac7df-926f-26a2-2b94-8c16560cd09d

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

@@ -43,7 +43,7 @@ class VCMDecodingState {
   uint32_t time_stamp() const;
   uint16_t sequence_num() const;
   // Return true if at initial state.
-  bool init() const;
+  bool in_initial_state() const;
   // Return true when sync is on - decode all layers.
   bool full_sync() const;
 
@@ -63,7 +63,7 @@ class VCMDecodingState {
   int         temporal_id_;
   int         tl0_pic_id_;
   bool        full_sync_;  // Sync flag when temporal layers are used.
-  bool        init_;
+  bool        in_initial_state_;
 };
 
 }  // namespace webrtc