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

net/server/http_server_unittest.cc

Index: net/server/http_server_unittest.cc
diff --git a/net/server/http_server_unittest.cc b/net/server/http_server_unittest.cc
index 03544f12b3d5f82a90c83ab5d8a0ba1cfbf2d4d7..c704d611ddcf6a3557d91b1ebc6382520e35dd75 100644
--- a/net/server/http_server_unittest.cc
+++ b/net/server/http_server_unittest.cc
@@ -546,6 +546,10 @@ class MockStreamSocket : public StreamSocket {
   }
   int SetSendBufferSize(int32_t size) override { return ERR_NOT_IMPLEMENTED; }
 
+  int SetDoNotFragment(bool do_not_fragment) override {
+    return ERR_NOT_IMPLEMENTED;
+  }
+
   void DidRead(const char* data, int data_len) {
     if (!read_buf_.get()) {
       pending_read_data_.append(data, data_len);