[cast_channel] Make CastSocketService a global leaky singleton

components/cast_channel/cast_socket.cc

Index: components/cast_channel/cast_socket.cc
diff --git a/components/cast_channel/cast_socket.cc b/components/cast_channel/cast_socket.cc
index 86adf570b84915e419ba27aa6c084d5c95168985..4039ade108f6b53bfbd437014fca434509805525 100644
--- a/components/cast_channel/cast_socket.cc
+++ b/components/cast_channel/cast_socket.cc
@@ -296,6 +296,11 @@ void CastSocketImpl::AddObserver(Observer* observer) {
     observers_.AddObserver(observer);
 }
 
+void CastSocketImpl::RemoveObserver(Observer* observer) {
+  DCHECK(observer);
+  observers_.RemoveObserver(observer);
+}
+
 void CastSocketImpl::OnConnectTimeout() {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
   // Stop all pending connection setup tasks and report back to the client.