Refactor WebCrypto code

content/child/webcrypto/platform_crypto.h

Index: content/child/webcrypto/platform_crypto.h
diff --git a/content/child/webcrypto/platform_crypto.h b/content/child/webcrypto/platform_crypto.h
index 9e957301c01a03d7f8feecac67350a9a8c4cc758..0ed16dc56b821c6f8313f3a4f8c0799db99eabe2 100644
--- a/content/child/webcrypto/platform_crypto.h
+++ b/content/child/webcrypto/platform_crypto.h
@@ -224,7 +224,9 @@ Status ImportRsaPrivateKey(const blink::WebCryptoAlgorithm& algorithm,
 
 // Note that this may be called from target Blink thread.
 // Preconditions:
+//  * algorithm is for an asymmetric algorithm
 //  * usage_mask makes sense for the algorithm.
+//  * key_data is not zero-length.
 Status ImportKeySpki(const blink::WebCryptoAlgorithm& algorithm,
                      const CryptoData& key_data,
                      bool extractable,
@@ -233,7 +235,9 @@ Status ImportKeySpki(const blink::WebCryptoAlgorithm& algorithm,
 
 // Note that this may be called from target Blink thread.
 // Preconditions:
+//  * algorithm is for an asymmetric algorithm
 //  * usage_mask makes sense for the algorithm.
+//  * key_data is not zero-length.
 Status ImportKeyPkcs8(const blink::WebCryptoAlgorithm& algorithm,
                       const CryptoData& key_data,
                       bool extractable,