IWYU fixes for url/...

url/url_canon_stdstring.cc

 // Copyright 2013 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 "url/url_canon_stdstring.h"
 
+#include <stddef.h>
+
 namespace url {
 
 StdStringCanonOutput::StdStringCanonOutput(std::string* str)
     : CanonOutput(), str_(str) {
   cur_len_ = static_cast<int>(str_->size());  // Append to existing data.
   str_->resize(str_->capacity());
   buffer_ = str_->empty() ? NULL : &(*str_)[0];
   buffer_len_ = static_cast<int>(str_->size());
 }
 
 StdStringCanonOutput::~StdStringCanonOutput() {
   // Nothing to do, we don't own the string.
 }
 
 void StdStringCanonOutput::Complete() {
   str_->resize(cur_len_);
   buffer_len_ = cur_len_;
 }
 
 void StdStringCanonOutput::Resize(int sz) {
   str_->resize(sz);
   buffer_ = str_->empty() ? NULL : &(*str_)[0];
   buffer_len_ = sz;
 }
 
 }  // namespace url