Add sanity check to generateKey to make sure usages aren't empty

content/child/webcrypto/algorithm_dispatch.cc

Index: content/child/webcrypto/algorithm_dispatch.cc
diff --git a/content/child/webcrypto/algorithm_dispatch.cc b/content/child/webcrypto/algorithm_dispatch.cc
index 1c9b409ace58e4cf87aa1dfa7014a4e46bb6aec4..c86ccd3781206234efec9346ac2eb6ae48d26947 100644
--- a/content/child/webcrypto/algorithm_dispatch.cc
+++ b/content/child/webcrypto/algorithm_dispatch.cc
@@ -8,6 +8,7 @@
 #include "content/child/webcrypto/algorithm_implementation.h"
 #include "content/child/webcrypto/algorithm_registry.h"
 #include "content/child/webcrypto/crypto_data.h"
+#include "content/child/webcrypto/generate_key_result.h"
 #include "content/child/webcrypto/platform_crypto.h"
 #include "content/child/webcrypto/status.h"
 #include "content/child/webcrypto/webcrypto_util.h"
@@ -111,7 +112,30 @@ Status GenerateKey(const blink::WebCryptoAlgorithm& algorithm,
   if (status.IsError())
     return status;
 
-  return impl->GenerateKey(algorithm, extractable, usages, result);
+  status = impl->GenerateKey(algorithm, extractable, usages, result);
+  if (status.IsError())
+    return status;
+
+  const blink::WebCryptoKey* key = NULL;
+  if (result->type() == GenerateKeyResult::TYPE_SECRET_KEY)
+    key = &result->secret_key();
+  if (result->type() == GenerateKeyResult::TYPE_PUBLIC_PRIVATE_KEY_PAIR)
+    key = &result->private_key();
+  if (key == NULL)
+    return Status::ErrorUnexpected();
+
+  // This should only fail if an algorithm is implemented incorrectly and
+  // does not do its own check of the usages.
+  if (key->usages() == 0) {
+    DCHECK(false) << "Key usages for generateKey() must not be empty";
+
+    // Even though this is unexpected, I chose not to use

[eroman, 2014/12/05 23:49:48]

Remove this comment. "I" will become unclear over time. I also think the TODO is
unnecessary.
I think the comment above is sufficient.

[nharper, 2014/12/05 23:58:08]

Done.

+    // Status::ErrorUnexpected() so that we can present a better error to the
+    // user.
+    // TODO(nharper): This should be instrumented with http://crbug.com/428806
+    return Status::ErrorCreateKeyEmptyUsages();
+  }
+  return status;
 }
 
 Status ImportKey(blink::WebCryptoKeyFormat format,