[Sync] Don't crash for encryption errors

sync/util/cryptographer.cc

Index: sync/util/cryptographer.cc
diff --git a/sync/util/cryptographer.cc b/sync/util/cryptographer.cc
index c22f0a322e6b0008f3f8aec3d336119aeb96594a..bccf9a28bd8ebbb2b0f90e7cb5e518f6f3c6b5ae 100644
--- a/sync/util/cryptographer.cc
+++ b/sync/util/cryptographer.cc
@@ -127,8 +127,10 @@ std::string Cryptographer::DecryptToString(
     const sync_pb::EncryptedData& encrypted) const {
   NigoriMap::const_iterator it = nigoris_.find(encrypted.key_name());
   if (nigoris_.end() == it) {
-    NOTREACHED() << "Cannot decrypt message";
-    return std::string();  // Caller should have called CanDecrypt(encrypt).
+    // The key used to encrypt the blob is not part of the set of installed
+    // nigoris.
+    LOG(ERROR) << "Cannot decrypt message";
+    return std::string();
   }
 
   std::string plaintext;