[webcryto] Validate key usages during key creation.

content/child/webcrypto/webcrypto_util.h

Index: content/child/webcrypto/webcrypto_util.h
diff --git a/content/child/webcrypto/webcrypto_util.h b/content/child/webcrypto/webcrypto_util.h
index ea0b0b3006e0700b9146de85a5aca27e57f99190..b903c8e626b358a24e9ce9fef39d6dd08ab79642 100644
--- a/content/child/webcrypto/webcrypto_util.h
+++ b/content/child/webcrypto/webcrypto_util.h
@@ -71,6 +71,10 @@ bool CreateSecretKeyAlgorithm(const blink::WebCryptoAlgorithm& algorithm,
                               unsigned int keylen_bytes,
                               blink::WebCryptoKeyAlgorithm* key_algorithm);
 
+// Returns true if the set bits in b make up a subset of the set bits in a.
+bool ContainsKeyUsages(blink::WebCryptoKeyUsageMask a,
+                       blink::WebCryptoKeyUsageMask b);
+
 }  // namespace webcrypto
 
 }  // namespace content