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

content/child/webcrypto/nss/sym_key_nss.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/child/webcrypto/nss/sym_key_nss.h"
 
 #include "base/logging.h"
 #include "content/child/webcrypto/crypto_data.h"
 #include "content/child/webcrypto/generate_key_result.h"
 #include "content/child/webcrypto/nss/key_nss.h"
@@ skipping 25 matching lines @@
   if (!pk11_key)
     return Status::OperationError();
 
   if (PK11_ExtractKeyValue(pk11_key.get()) != SECSuccess)
     return Status::OperationError();
 
   const SECItem* key_data = PK11_GetKeyData(pk11_key.get());
   if (!key_data)
     return Status::OperationError();
 
+  // TODO(nharper): mask usages with allowed usages

[eroman, 2014/11/20 23:40:10]

Testing the allowed usages is the responsibility of the caller of
GenerateSecretKeyNss, so I don't think this TODO is necessary.

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

Done.

+  if (usages == 0) {

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

The style being used in these files is that single line if statements omit
braces. Please match it for new code.

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

Done.

+    return Status::ErrorCreateKeyBadUsages();

[eroman, 2014/11/20 23:40:10]

Introduce a new error message so this is easier to understand for web
developers.

Perhaps:
 Status::ErrorGenerateKeyEmptyUsages()

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

Done.

+  }
+
   scoped_ptr<SymKeyNss> handle(new SymKeyNss(
       pk11_key.Pass(), CryptoData(key_data->data, key_data->len)));
 
   result->AssignSecretKey(
       blink::WebCryptoKey::create(handle.release(),
                                   blink::WebCryptoKeyTypeSecret,
                                   extractable,
                                   algorithm,
                                   usages));
 
@@ skipping 29 matching lines @@
                                      blink::WebCryptoKeyTypeSecret,
                                      extractable,
                                      algorithm,
                                      usages);
   return Status::Success();
 }
 
 }  // namespace webcrypto
 
 }  // namespace content