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

net/spdy/array_output_buffer.h

 // Copyright 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_ARRAY_OUTPUT_BUFFER_H_
 #define NET_SPDY_ARRAY_OUTPUT_BUFFER_H_
 
-#include <string.h>
+#include <cstddef>
 #include "net/spdy/zero_copy_output_buffer.h"
 
 namespace net {
 
 class ArrayOutputBuffer : public ZeroCopyOutputBuffer {
  public:
   // |buffer| is pointed to the output to write to, and |size| is the capacity
   // of the output.
   ArrayOutputBuffer(char* buffer, int64_t size)
       : current_(buffer), begin_(buffer), capacity_(size) {}
@@ skipping 12 matching lines @@
 
  private:
   char* current_ = nullptr;
   char* begin_ = nullptr;
   int64_t capacity_ = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_SPDY_ARRAY_OUTPUT_BUFFER_H_