Revert of Only compare sequence numbers from the same SSRC in ForwardErrorCorrection.

webrtc/modules/rtp_rtcp/source/forward_error_correction.h

Index: webrtc/modules/rtp_rtcp/source/forward_error_correction.h
diff --git a/webrtc/modules/rtp_rtcp/source/forward_error_correction.h b/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
index e5a38b6c006cfd88033e1edd858a69d9ddf4d703..f45473cb1f417cbb36dcdabb0f2c99542af9ccca 100644
--- a/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
+++ b/webrtc/modules/rtp_rtcp/source/forward_error_correction.h
@@ -62,25 +62,29 @@
   class SortablePacket {
    public:
     // Functor which returns true if the sequence number of |first|
-    // is < the sequence number of |second|. Should only ever be called for
-    // packets belonging to the same SSRC.
+    // is < the sequence number of |second|.
     struct LessThan {
       template <typename S, typename T>
       bool operator() (const S& first, const T& second);
     };
 
-    uint32_t ssrc;
     uint16_t seq_num;
   };
 
   // The received list parameter of DecodeFec() references structs of this type.
   //
+  // The ssrc member is needed to ensure that we can restore the SSRC field of
+  // recovered packets. In most situations this could be retrieved from other
+  // media packets, but in the case of an FEC packet protecting a single
+  // missing media packet, we have no other means of obtaining it.
   // TODO(holmer): Refactor into a proper class.
   class ReceivedPacket : public SortablePacket {
    public:
     ReceivedPacket();
     ~ReceivedPacket();
 
+    uint32_t ssrc;  // SSRC of the current frame. Must be set for FEC
+                    // packets, but not required for media packets.
     bool is_fec;    // Set to true if this is an FEC packet and false
                     // otherwise.
     rtc::scoped_refptr<Packet> pkt;  // Pointer to the packet storage.
@@ -105,7 +109,7 @@
   // Used to link media packets to their protecting FEC packets.
   //
   // TODO(holmer): Refactor into a proper class.
-  class ProtectedPacket : public SortablePacket {
+  class ProtectedPacket : public ForwardErrorCorrection::SortablePacket {
    public:
     ProtectedPacket();
     ~ProtectedPacket();
@@ -118,7 +122,7 @@
   // Used for internal storage of received FEC packets in a list.
   //
   // TODO(holmer): Refactor into a proper class.
-  class ReceivedFecPacket : public SortablePacket {
+  class ReceivedFecPacket : public ForwardErrorCorrection::SortablePacket {
    public:
     ReceivedFecPacket();
     ~ReceivedFecPacket();