Replace ToLower calls to the new format

chromeos/cryptohome/system_salt_getter.cc

Index: chromeos/cryptohome/system_salt_getter.cc
diff --git a/chromeos/cryptohome/system_salt_getter.cc b/chromeos/cryptohome/system_salt_getter.cc
index 9c2e2449eb8327ae492be634d11fa98a57ae1a6b..b0bbc9e9b8261c833cf5ce73dc469314de721f34 100644
--- a/chromeos/cryptohome/system_salt_getter.cc
+++ b/chromeos/cryptohome/system_salt_getter.cc
@@ -95,8 +95,8 @@ SystemSaltGetter* SystemSaltGetter::Get() {
 // static
 std::string SystemSaltGetter::ConvertRawSaltToHexString(
     const std::vector<uint8>& salt) {
-  return base::StringToLowerASCII(base::HexEncode(
-      reinterpret_cast<const void*>(salt.data()), salt.size()));
+  return base::ToLowerASCII(
+      base::HexEncode(reinterpret_cast<const void*>(salt.data()), salt.size()));
 }
 
 }  // namespace chromeos