Reland of SSRC and RSID may only refer to one sink each in RtpDemuxer

webrtc/call/rtp_rtcp_demuxer_helper.h

Index: webrtc/call/rtp_rtcp_demuxer_helper.h
diff --git a/webrtc/call/rtp_rtcp_demuxer_helper.h b/webrtc/call/rtp_rtcp_demuxer_helper.h
index 4791e55ca39e153fd2c2c701544f1b38848098b9..85204365fb5b14b1704b3d212aafde588939f6f7 100644
--- a/webrtc/call/rtp_rtcp_demuxer_helper.h
+++ b/webrtc/call/rtp_rtcp_demuxer_helper.h
@@ -21,6 +21,7 @@
 
 namespace webrtc {
 
+// TODO(eladalon): Remove this in the next CL.
 template <typename Container>
 bool MultimapAssociationExists(const Container& multimap,
                                const typename Container::key_type& key,
@@ -31,6 +32,7 @@
                      [val](Reference elem) { return elem.second == val; });
 }
 
+// TODO(eladalon): Remove this in the next CL.
 template <typename Container, typename Value>
 size_t RemoveFromMultimapByValue(Container* multimap, const Value& value) {
   size_t count = 0;
@@ -45,11 +47,26 @@
   return count;
 }
 
+template <typename Map, typename Value>
+size_t RemoveFromMapByValue(Map* map, const Value& value) {
+  size_t count = 0;
+  for (auto it = map->begin(); it != map->end();) {
+    if (it->second == value) {
+      it = map->erase(it);
+      ++count;
+    } else {
+      ++it;
+    }
+  }
+  return count;
+}
+
 template <typename Container, typename Key>
 bool ContainerHasKey(const Container& c, const Key& k) {
   return std::find(c.cbegin(), c.cend(), k) != c.cend();
 }
 
+// TODO(eladalon): Remove this in the next CL.
 template <typename Container>
 bool MultimapHasValue(const Container& c,
                       const typename Container::mapped_type& v) {
@@ -59,6 +76,14 @@
   return std::any_of(c.cbegin(), c.cend(), predicate);
 }
 
+template <typename Map>
+bool MapHasValue(const Map& map, const typename Map::mapped_type& value) {
+  auto predicate = [value](const typename Map::value_type& it) {
+    return it.second == value;
+  };
+  return std::any_of(map.cbegin(), map.cend(), predicate);
+}
+
 rtc::Optional<uint32_t> ParseRtcpPacketSenderSsrc(
     rtc::ArrayView<const uint8_t> packet);