Allow QuicClient to set connection MTU before the handshake is sent.

net/tools/quic/test_tools/limited_mtu_test_writer.cc

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/tools/quic/test_tools/limited_mtu_test_writer.h"
+
+namespace net {
+namespace tools {
+namespace test {
+
+LimitedMtuTestWriter::LimitedMtuTestWriter(QuicByteCount mtu) : mtu_(mtu) {}
+
+LimitedMtuTestWriter::~LimitedMtuTestWriter() {}
+
+WriteResult LimitedMtuTestWriter::WritePacket(
+    const char* buffer,
+    size_t buf_len,
+    const IPAddressNumber& self_address,
+    const IPEndPoint& peer_address) {
+  if (buf_len > mtu_) {
+    // Drop the packet.
+    return WriteResult(WRITE_STATUS_OK, buf_len);
+  }
+
+  return QuicPacketWriterWrapper::WritePacket(buffer, buf_len, self_address,
+                                              peer_address);
+}
+
+}  // namespace test
+}  // namespace tools
+}  // namespace net