Correct const accessors in base/values.(h|cc), Part II (ListValue)

ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc

Index: ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc
diff --git a/ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc b/ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc
index 5bf74cb8f8468087f7cb41982ceed3a2c6b5506b..d3454eada7db6877ef8244a181c73cb192d83ce1 100644
--- a/ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc
+++ b/ppapi/shared_impl/private/ppb_x509_certificate_private_shared.cc
@@ -30,7 +30,7 @@ void PPB_X509Certificate_Fields::SetField(
 PP_Var PPB_X509Certificate_Fields::GetFieldAsPPVar(
     PP_X509Certificate_Private_Field field) const {
   uint32_t index = static_cast<uint32_t>(field);
-  base::Value* value;
+  const base::Value* value;
   bool success = values_.Get(index, &value);
   if (!success) {
     // Our list received might be smaller than the number of fields, so just