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

net/dns/address_sorter_posix_unittest.cc

Index: net/dns/address_sorter_posix_unittest.cc
diff --git a/net/dns/address_sorter_posix_unittest.cc b/net/dns/address_sorter_posix_unittest.cc
index 88a135fef9d82a011d0b0b05161259745e530da4..a21ba6b292b208f63128d4052c7bfcfda0ef3012 100644
--- a/net/dns/address_sorter_posix_unittest.cc
+++ b/net/dns/address_sorter_posix_unittest.cc
@@ -46,7 +46,7 @@ class TestUDPClientSocket : public DatagramClientSocket {
   int SetReceiveBufferSize(int32) override { return OK; }
   int SetSendBufferSize(int32) override { return OK; }
 
-  void Close() override {}
+  int Close() override { return OK; }
   int GetPeerAddress(IPEndPoint* address) const override {
     NOTIMPLEMENTED();
     return OK;