Negotiating Simulcast in the initial offer/answer - Part1.

This change adds Simulcast negotiation to media session offers/answers.
Next step is to add negotiation logic to PeerConnection.

Bug: webrtc:10075
Change-Id: Iea3a1084c16058f0efbc974cf623ec05c3c7a74f
Reviewed-on: https://webrtc-review.googlesource.com/c/115790
Reviewed-by: Seth Hampson <shampson@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Amit Hilbuch <amithi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26115}
diff --git a/pc/simulcastdescription.cc b/pc/simulcastdescription.cc
index 8fff520..61849ce 100644
--- a/pc/simulcastdescription.cc
+++ b/pc/simulcastdescription.cc
@@ -20,6 +20,10 @@
   RTC_DCHECK(!rid.empty());
 }
 
+bool SimulcastLayer::operator==(const SimulcastLayer& other) const {
+  return rid == other.rid && is_paused == other.is_paused;
+}
+
 void SimulcastLayerList::AddLayer(const SimulcastLayer& layer) {
   list_.push_back({layer});
 }