Update JSONReader to take base::StringPiece instead of std::string

base/json/json_reader.cc

Index: base/json/json_reader.cc
diff --git a/base/json/json_reader.cc b/base/json/json_reader.cc
index fb1459b4ceb33aa42225c431888c8f2767a5dc53..593273ebd44f03f98f8cfdda0fda5ec54a6900da 100644
--- a/base/json/json_reader.cc
+++ b/base/json/json_reader.cc
@@ -38,20 +38,20 @@ JSONReader::~JSONReader() {
 }
 
 // static
-Value* JSONReader::Read(const std::string& json) {
+Value* JSONReader::Read(const StringPiece& json) {
   internal::JSONParser parser(JSON_PARSE_RFC);
   return parser.Parse(json);
 }
 
 // static
-Value* JSONReader::Read(const std::string& json,
+Value* JSONReader::Read(const StringPiece& json,
                         int options) {
   internal::JSONParser parser(options);
   return parser.Parse(json);
 }
 
 // static
-Value* JSONReader::ReadAndReturnError(const std::string& json,
+Value* JSONReader::ReadAndReturnError(const StringPiece& json,
                                       int options,
                                       int* error_code_out,
                                       std::string* error_msg_out) {