chore(ext/webidl): Add dictionary converter microbenchmark (#17435)

This commits add a `webidl.createDictionaryConverter` converter
microbenchmark.

There are 2 PRs currently open that need a microbenchmark for webidl
dictionary converter. See https://github.com/denoland/deno/pull/16594
and https://github.com/denoland/deno/pull/16407

Closes https://github.com/denoland/deno/issues/17436

1 files changed, 35 insertions, 0 deletions

diff --git a/ext/webidl/benches/dict.js b/ext/webidl/benches/dict.js
new file mode 100644
index 000000000..353a630eb
--- /dev/null
+++ b/ext/webidl/benches/dict.js
@@ -0,0 +1,35 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+// deno-lint-ignore-file
+
+const { createDictionaryConverter, converters } = globalThis.__bootstrap.webidl;
+
+const TextDecodeOptions = createDictionaryConverter(
+  "TextDecodeOptions",
+  [
+    {
+      key: "stream",
+      converter: converters.boolean,
+      defaultValue: false,
+    },
+  ],
+);
+
+// Sanity check
+{
+  const o = TextDecodeOptions(undefined);
+  if (o.stream !== false) {
+    throw new Error("Unexpected stream value");
+  }
+}
+
+function handwrittenConverter(V) {
+  const defaultValue = { stream: false };
+  if (V === undefined || V === null) {
+    return defaultValue;
+  }
+  if (V.stream !== undefined) {
+    defaultValue.stream = !!V.stream;
+  }
+  return defaultValue;
+}