Revert "third_party/protobuf: Update to HEAD (83d681ee2c)"

third_party/protobuf/src/google/protobuf/util/internal/json_escaping.cc

 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
@@ skipping 237 matching lines @@
 // and returns a StringPiece that points to this buffer. The input buffer needs
 // to be at least 6 bytes long.
 StringPiece ToHex(uint16 cp, char* buffer) {
   buffer[5] = kHex[cp & 0x0f];
   cp >>= 4;
   buffer[4] = kHex[cp & 0x0f];
   cp >>= 4;
   buffer[3] = kHex[cp & 0x0f];
   cp >>= 4;
   buffer[2] = kHex[cp & 0x0f];
-  return StringPiece(buffer).substr(0, 6);
+  return StringPiece(buffer, 0, 6);
 }
 
 // Stores the 32-bit unicode code point as its hexadecimal digits in buffer
 // and returns a StringPiece that points to this buffer. The input buffer needs
 // to be at least 12 bytes long.
 StringPiece ToSurrogateHex(uint32 cp, char* buffer) {
   uint16 low = ToLowSurrogate(cp);
   uint16 high = ToHighSurrogate(cp);
 
   buffer[11] = kHex[low & 0x0f];
@@ skipping 126 matching lines @@
   if (num_left > 0) {
     // Treat as case iii: report error.
     // TODO(wpoon): Add error reporting.
   }
 }
 
 }  // namespace converter
 }  // namespace util
 }  // namespace protobuf
 }  // namespace google