[webcrypto] Change HMAC key generation length from bytes to bits.

content/child/webcrypto/shared_crypto.cc

Index: content/child/webcrypto/shared_crypto.cc
diff --git a/content/child/webcrypto/shared_crypto.cc b/content/child/webcrypto/shared_crypto.cc
index cffdcc54dd9dc5290db18c08244ba8274e394d9b..580754ae47966343874aee1766ea68b8d2672d52 100644
--- a/content/child/webcrypto/shared_crypto.cc
+++ b/content/child/webcrypto/shared_crypto.cc
@@ -315,8 +315,15 @@ Status GenerateSecretKey(const blink::WebCryptoAlgorithm& algorithm,
       const blink::WebCryptoHmacKeyGenParams* params =
           algorithm.hmacKeyGenParams();
       DCHECK(params);
+#if defined(WEBCRYPTO_HMAC_BITS)
+      if (params->hasLengthBits()) {
+        if (params->optionalLengthBits() % 8)
+          return Status::ErrorGenerateKeyLength();
+        keylen_bytes = params->optionalLengthBits() / 8;
+#else
       if (params->hasLengthBytes()) {
         keylen_bytes = params->optionalLengthBytes();
+#endif
       } else {
         keylen_bytes = ShaBlockSizeBytes(params->hash().id());
         if (keylen_bytes == 0)