Update from https://crrev.com/315085

base/json/json_string_value_serializer.cc

Index: base/json/json_string_value_serializer.cc
diff --git a/base/json/json_string_value_serializer.cc b/base/json/json_string_value_serializer.cc
index 59f030dff2fd52418333218bcaeb3868295994be..b626640a1bfc646b15f09e4c548045ea0758266e 100644
--- a/base/json/json_string_value_serializer.cc
+++ b/base/json/json_string_value_serializer.cc
@@ -10,6 +10,21 @@
 
 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) {
@@ -23,7 +38,7 @@ bool JSONStringValueSerializer::SerializeAndOmitBinaryValues(
 
 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;
@@ -37,10 +52,7 @@ bool JSONStringValueSerializer::SerializeInternal(const Value& root,
 
 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);