webcrypto: Add ECDSA algorithm (chromium-side)

content/child/webcrypto/jwk.h

Index: content/child/webcrypto/jwk.h
diff --git a/content/child/webcrypto/jwk.h b/content/child/webcrypto/jwk.h
index cb6866df178a126535b748ff91127a6f23817d38..588fb98bdb58c1199c89c91b64b2b194eb7fdf6d 100644
--- a/content/child/webcrypto/jwk.h
+++ b/content/child/webcrypto/jwk.h
@@ -108,6 +108,8 @@ class JwkReader {
 class JwkWriter {
  public:
   // Initializes a writer, and sets the standard JWK members as indicated.
+  // |algorithm| is optional, and is only written if the provided |algorithm| is
+  // non-empty.
   JwkWriter(const std::string& algorithm,
             bool extractable,
             blink::WebCryptoKeyUsageMask usages,