[cast_channel] Make CastMessageHandler a CastSocket::Observer instead of CastTransport::Delegate

components/cast_channel/cast_socket_service.cc

Index: components/cast_channel/cast_socket_service.cc
diff --git a/components/cast_channel/cast_socket_service.cc b/components/cast_channel/cast_socket_service.cc
index f58c9858e9212121ed2ad48758d411773747d708..5da94186046d554d355e2ac58d9ec0173cf5058f 100644
--- a/components/cast_channel/cast_socket_service.cc
+++ b/components/cast_channel/cast_socket_service.cc
@@ -52,6 +52,19 @@ CastSocket* CastSocketService::GetSocket(int channel_id) const {
   return socket_it == sockets_.end() ? nullptr : socket_it->second.get();
 }
 
+CastSocket::Observer* CastSocketService::GetObserver(const std::string& id) {
+  auto it = socket_observer_map_.find(id);
+  return it == socket_observer_map_.end() ? nullptr : it->second.get();
+}
+
+CastSocket::Observer* CastSocketService::AddObserver(
+    const std::string& id,
+    std::unique_ptr<CastSocket::Observer> observer) {
+  CastSocket::Observer* observer_ptr = observer.get();
+  socket_observer_map_.insert(std::make_pair(id, std::move(observer)));
+  return observer_ptr;
+}
+
 void CastSocketService::ShutdownOnUIThread() {}
 
 }  // namespace cast_channel