Refactor: Extract common code for generating asymmetric keys to a helper.

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 7a35593c18bdd75b2bfd5d7cd6e29704aa5f069b..388a585ea5b2cef6608ccfdb14fd053eaacf5149 100644
--- a/content/child/webcrypto/nss/rsa_key_nss.cc
+++ b/content/child/webcrypto/nss/rsa_key_nss.cc
@@ -503,19 +503,15 @@ Status RsaHashedAlgorithm::GenerateKey(
     bool extractable,
     blink::WebCryptoKeyUsageMask combined_usages,
     GenerateKeyResult* result) const {
-  Status status = CheckKeyCreationUsages(
-      all_public_key_usages_ | all_private_key_usages_, combined_usages);
+  blink::WebCryptoKeyUsageMask public_usages = 0;
+  blink::WebCryptoKeyUsageMask private_usages = 0;
+
+  Status status = GetUsagesForGenerateAsymmetricKey(
+      all_public_key_usages_, all_private_key_usages_, combined_usages,
+      &public_usages, &private_usages);
   if (status.IsError())
     return status;
 
-  const blink::WebCryptoKeyUsageMask public_usages =
-      combined_usages & all_public_key_usages_;
-  const blink::WebCryptoKeyUsageMask private_usages =
-      combined_usages & all_private_key_usages_;
-
-  if (private_usages == 0)
-    return Status::ErrorCreateKeyEmptyUsages();
-
   unsigned int public_exponent = 0;
   unsigned int modulus_length_bits = 0;
   status = GetRsaKeyGenParameters(algorithm.rsaHashedKeyGenParams(),