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

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 fdfea99316d02933d3d9f503f25b09f6beb630a6..8866c08d953cd210f9179e907dd486b01b9c15a3 100644
--- a/content/child/webcrypto/webcrypto_util.h
+++ b/content/child/webcrypto/webcrypto_util.h
@@ -81,6 +81,16 @@ Status GetRsaKeyGenParameters(
     unsigned int* public_exponent,
     unsigned int* modulus_length_bits);
 
+// Splits the combined usages given to GenerateKey() into the respective usages
+// for the public key and private key. Returns an error if the usages are
+// invalid.
+Status GetUsagesForGenerateAsymmetricKey(
+    blink::WebCryptoKeyUsageMask combined_usages,
+    blink::WebCryptoKeyUsageMask all_public_usages,
+    blink::WebCryptoKeyUsageMask all_private_usages,
+    blink::WebCryptoKeyUsageMask* public_usages,
+    blink::WebCryptoKeyUsageMask* private_usages);
+
 }  // namespace webcrypto
 
 }  // namespace content