Update from https://crrev.com/333737

base/json/string_escape.cc

 // Copyright (c) 2006-2008 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 "base/json/string_escape.h"
 
 #include <string>
 
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ skipping 117 matching lines @@
 }
 
 std::string EscapeBytesAsInvalidJSONString(const StringPiece& str,
                                            bool put_in_quotes) {
   std::string dest;
 
   if (put_in_quotes)
     dest.push_back('"');
 
   for (StringPiece::const_iterator it = str.begin(); it != str.end(); ++it) {
-    ToUnsigned<StringPiece::value_type>::Unsigned c = *it;
+    unsigned char c = *it;
     if (EscapeSpecialCodePoint(c, &dest))
       continue;
 
     if (c < 32 || c > 126)
       base::StringAppendF(&dest, kU16EscapeFormat, c);
     else
       dest.push_back(*it);
   }
 
   if (put_in_quotes)
     dest.push_back('"');
 
   return dest;
 }
 
 }  // namespace base