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

content/child/webcrypto/openssl/util_openssl.cc

Index: content/child/webcrypto/openssl/util_openssl.cc
diff --git a/content/child/webcrypto/openssl/util_openssl.cc b/content/child/webcrypto/openssl/util_openssl.cc
index 665e1525ff1f267dd024eb8cb4669e840ff1bf01..78e116d13eeb45b2912721b5d4499d58cf76b567 100644
--- a/content/child/webcrypto/openssl/util_openssl.cc
+++ b/content/child/webcrypto/openssl/util_openssl.cc
@@ -180,6 +180,8 @@ Status CreateWebCryptoPrivateKey(crypto::ScopedEVP_PKEY private_key,
   *key = blink::WebCryptoKey::create(
       new AsymKeyOpenSsl(private_key.Pass(), CryptoData(pkcs8_data)),
       blink::WebCryptoKeyTypePrivate, extractable, algorithm, usages);
+  if (key->usages() == 0)

[eroman, 2014/11/21 23:35:34]

Per our discussion this is best left to a follow-up patch since it has
implications on structured (de-)cloning.

Also we should fail faster (before doing the PKCS8 export)

[nharper, 2014/11/22 00:26:45]

I moved this check up to the GenerateKey() functions that call
CreateWebCryptoPrivateKey(), and put it right after they define private_usages.

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