Add CHECK() in UdpSocketLibevent to debug crbug.com/452121

net/udp/udp_socket_libevent.cc

Index: net/udp/udp_socket_libevent.cc
diff --git a/net/udp/udp_socket_libevent.cc b/net/udp/udp_socket_libevent.cc
index a36c59b4d64c37a459857c55be34803f04ecbcb0..7951155c0e6799697991590e15fc9436d286ba4c 100644
--- a/net/udp/udp_socket_libevent.cc
+++ b/net/udp/udp_socket_libevent.cc
@@ -105,11 +105,11 @@ int UDPSocketLibevent::Open(AddressFamily address_family) {
   return OK;
 }
 
-void UDPSocketLibevent::Close() {
+int UDPSocketLibevent::Close() {
   DCHECK(CalledOnValidThread());
 
   if (socket_ == kInvalidSocket)
-    return;
+    return OK;
 
   // Zero out any pending read/write callback state.
   read_buf_ = NULL;
@@ -126,12 +126,17 @@ void UDPSocketLibevent::Close() {
   ok = write_socket_watcher_.StopWatchingFileDescriptor();
   DCHECK(ok);
 
-  if (IGNORE_EINTR(close(socket_)) < 0)
+  int result = OK;
+  if (IGNORE_EINTR(close(socket_)) < 0) {
     PLOG(ERROR) << "close";
+    result = MapSystemError(errno);
+  }
 
   socket_ = kInvalidSocket;
   addr_family_ = 0;
   is_connected_ = false;
+
+  return result;
 }
 
 int UDPSocketLibevent::GetPeerAddress(IPEndPoint* address) const {