Check that usage isn't empty when generateKey() is called

content/child/webcrypto/nss/rsa_key_nss.cc

Index: content/child/webcrypto/nss/rsa_key_nss.cc
diff --git a/content/child/webcrypto/nss/rsa_key_nss.cc b/content/child/webcrypto/nss/rsa_key_nss.cc
index 129d5e42b3b845f0abfca4bd49a2ebad74276b6d..a2d7185bb09e50e8f053f7b265f2fe249f3bf892 100644
--- a/content/child/webcrypto/nss/rsa_key_nss.cc
+++ b/content/child/webcrypto/nss/rsa_key_nss.cc
@@ -602,6 +602,9 @@ Status RsaHashedAlgorithm::GenerateKey(
                                   private_usages);
 
   result->AssignKeyPair(public_key, private_key);
+  if (result->private_key().usages() == 0) {

[eroman, 2014/11/20 23:40:09]

Move the failure to before the key has been generated.

This is a bit different with respect to which errors will be given when there
are multiple problems, but should be fine.

(Alternately if we were OK doing the test after key generation, the logic could
be moved to the global GenerateKey() function so it doesn't need to be
duplicated into each algorithm implementation. However early failure is more
useful).

[nharper, 2014/11/21 22:12:01]

Done.

+    return Status::ErrorCreateKeyBadUsages();
+  }
   return Status::Success();
 }