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 c9f6e76ffb6904d07afa6d5445bc49bac92eb472..e96b62ddb287076998a572d1e010ba85c9edf60e 100644
--- a/base/json/json_reader.cc
+++ b/base/json/json_reader.cc
@@ -93,13 +93,13 @@ JSONReader::JSONReader()
       error_col_(0) {}
 
 // static
-Value* JSONReader::Read(const std::string& json,
+Value* JSONReader::Read(const StringPiece& json,
                         bool allow_trailing_comma) {
   return ReadAndReturnError(json, allow_trailing_comma, NULL, NULL);
 }
 
 // static
-Value* JSONReader::ReadAndReturnError(const std::string& json,
+Value* JSONReader::ReadAndReturnError(const StringPiece& json,
                                       bool allow_trailing_comma,
                                       int* error_code_out,
                                       std::string* error_msg_out) {
@@ -148,7 +148,7 @@ std::string JSONReader::GetErrorMessage() const {
                             ErrorCodeToString(error_code_));
 }
 
-Value* JSONReader::JsonToValue(const std::string& json, bool check_root,
+Value* JSONReader::JsonToValue(const StringPiece& json, bool check_root,
                                bool allow_trailing_comma) {
   // The input must be in UTF-8.
   if (!IsStringUTF8(json.data())) {