Update from https://crrev.com/315085

base/json/json_string_value_serializer.cc

 // 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.
 
 #include "base/json/json_string_value_serializer.h"
 
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 
 using base::Value;
 
+JSONStringValueSerializer::JSONStringValueSerializer(std::string* json_string)
+    : json_string_(json_string),
+      json_string_readonly_(*json_string),
+      pretty_print_(false),
+      allow_trailing_comma_(false) {
+}
+
+JSONStringValueSerializer::JSONStringValueSerializer(
+    const base::StringPiece& json_string)
+    : json_string_(nullptr),
+      json_string_readonly_(json_string),
+      pretty_print_(false),
+      allow_trailing_comma_(false) {
+}
+
 JSONStringValueSerializer::~JSONStringValueSerializer() {}
 
 bool JSONStringValueSerializer::Serialize(const Value& root) {
   return SerializeInternal(root, false);
 }
 
 bool JSONStringValueSerializer::SerializeAndOmitBinaryValues(
     const Value& root) {
   return SerializeInternal(root, true);
 }
 
 bool JSONStringValueSerializer::SerializeInternal(const Value& root,
                                                   bool omit_binary_values) {
-  if (!json_string_ || initialized_with_const_string_)
+  if (!json_string_)
     return false;
 
   int options = 0;
   if (omit_binary_values)
     options |= base::JSONWriter::OPTIONS_OMIT_BINARY_VALUES;
   if (pretty_print_)
     options |= base::JSONWriter::OPTIONS_PRETTY_PRINT;
 
   return base::JSONWriter::WriteWithOptions(&root, options, json_string_);
 }
 
 Value* JSONStringValueSerializer::Deserialize(int* error_code,
                                               std::string* error_str) {
-  if (!json_string_)
-    return NULL;
-
-  return base::JSONReader::ReadAndReturnError(*json_string_,
+  return base::JSONReader::ReadAndReturnError(json_string_readonly_,
       allow_trailing_comma_ ? base::JSON_ALLOW_TRAILING_COMMAS :
           base::JSON_PARSE_RFC,
       error_code, error_str);
 }