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

net/spdy/spdy_frame_builder.h

 // Copyright (c) 2012 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_SPDY_FRAME_BUILDER_H_
 #define NET_SPDY_SPDY_FRAME_BUILDER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
-#include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/sys_byteorder.h"
 #include "net/base/net_export.h"
 #include "net/spdy/platform/api/spdy_string_piece.h"
 #include "net/spdy/spdy_bug_tracker.h"
 #include "net/spdy/spdy_protocol.h"
 #include "net/spdy/zero_copy_output_buffer.h"
 
 namespace net {
@@ skipping 121 matching lines @@
   const size_t kLengthFieldLength = 3;
   char* start_of_current_frame_ = nullptr;
   size_t bytes_of_length_written_in_first_block_ = kLengthFieldLength;
   // In case length of a new frame is cross blocks.
   char* start_of_current_frame_in_next_block_ = nullptr;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_SPDY_FRAME_BUILDER_H_