Add a SetDoNotFragment() method to DatagramSocket, and call this for

net/socket/client_socket_pool_base_unittest.cc

Index: net/socket/client_socket_pool_base_unittest.cc
diff --git a/net/socket/client_socket_pool_base_unittest.cc b/net/socket/client_socket_pool_base_unittest.cc
index 6eea7e1dc8fba0d6392a89fa002132bfa2f775dd..909738057093a39a2d680d7f278b56369f8c8494 100644
--- a/net/socket/client_socket_pool_base_unittest.cc
+++ b/net/socket/client_socket_pool_base_unittest.cc
@@ -154,6 +154,7 @@ class MockClientSocket : public StreamSocket {
   }
   int SetReceiveBufferSize(int32_t size) override { return OK; }
   int SetSendBufferSize(int32_t size) override { return OK; }
+  int SetDoNotFragment(bool do_not_fragment) override { return OK; }
 
   // StreamSocket implementation.
   int Connect(const CompletionCallback& callback) override {