Add SpdyString alias for std::string in net/spdy.

net/spdy/platform/api/spdy_string.h

Index: net/spdy/platform/api/spdy_string.h
diff --git a/net/spdy/platform/api/spdy_string.h b/net/spdy/platform/api/spdy_string.h
new file mode 100644
index 0000000000000000000000000000000000000000..59089a50b6eb0be433471a5225b12f8279585b78
--- /dev/null
+++ b/net/spdy/platform/api/spdy_string.h
@@ -0,0 +1,16 @@
+// Copyright (c) 2017 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_SPDY_PLATFORM_API_SPDY_STRING_H_
+#define NET_SPDY_PLATFORM_API_SPDY_STRING_H_
+
+#include "net/spdy/platform/impl/spdy_string_impl.h"
+
+namespace net {
+
+using SpdyString = SpdyStringImpl;
+
+}  // namespace net
+
+#endif  // NET_SPDY_PLATFORM_API_SPDY_STRING_H_