Add a TODO comment to describe when we can remove the const_cast for...

base/crypto/signature_creator_nss.cc

Index: base/crypto/signature_creator_nss.cc
===================================================================
--- base/crypto/signature_creator_nss.cc	(revision 27096)
+++ base/crypto/signature_creator_nss.cc	(working copy)
@@ -47,6 +47,8 @@
 }
 
 bool SignatureCreator::Update(const uint8* data_part, int data_part_len) {
+  // TODO(wtc): Remove this const_cast when we require NSS 3.12.5.
+  // See NSS bug https://bugzilla.mozilla.org/show_bug.cgi?id=518255
   SECStatus rv = SGN_Update(sign_context_,
                             const_cast<unsigned char*>(data_part),
                             data_part_len);