Add QuicStrCat.

net/quic/platform/impl/quic_str_cat_impl.h

+// Copyright (c) 2016 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.
+
+#ifndef NET_QUIC_PLATFORM_IMPL_QUIC_STR_CAT_IMPL_H_
+#define NET_QUIC_PLATFORM_IMPL_QUIC_STR_CAT_IMPL_H_
+
+#include <sstream>
+#include <string>
+
+namespace net {
+
+template <typename... Args>
+inline std::string QuicStrCatImpl(const Args&... args) {
+  std::ostringstream oss;
+  int dummy[] = {1, (oss << args, 0)...};
+  static_cast<void>(dummy);
+  return oss.str();
+}
+
+}  // namespace net
+
+#endif  // NET_QUIC_PLATFORM_IMPL_QUIC_STR_CAT_IMPL_H_