[webcryto] Validate key usages during key creation.

content/child/webcrypto/shared_crypto.h

Index: content/child/webcrypto/shared_crypto.h
diff --git a/content/child/webcrypto/shared_crypto.h b/content/child/webcrypto/shared_crypto.h
index 57627d60b0dad359a47ce5a620517ab5d95a9fd2..d9e5a959db71e4a8a697a49b6be2c63614975ece 100644
--- a/content/child/webcrypto/shared_crypto.h
+++ b/content/child/webcrypto/shared_crypto.h
@@ -174,6 +174,12 @@ Status ToPlatformPublicKey(const blink::WebCryptoKey& key,
 Status ToPlatformPrivateKey(const blink::WebCryptoKey& key,
                             platform::PrivateKey** out);
 
+// Returns Staus::Success() if |usages| is valid for |key_type| and |algorithm|.
+// Otherwise returns a failure
+Status CheckKeyUsages(blink::WebCryptoAlgorithmId algorithm,
+                      blink::WebCryptoKeyType key_type,
+                      blink::WebCryptoKeyUsageMask usages);
+
 }  // namespace webcrypto
 
 }  // namespace content