Bug 1769626 [wpt PR 34080] - Add (missing) platform member to NavigatorUAData.toJSON output, a=testonly

Automatic update from web-platform-tests
Add (missing) platform member to NavigatorUAData.toJSON output

As platform is a low-entropy hint, it should have been included
originally (but seems to have been forgotten).

Bug: 1323565
Change-Id: Ic72048144cc335fdc57652ec544105c3ad38e5cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3646649
Reviewed-by: Dominic Farolino <dom@chromium.org>
Reviewed-by: Victor Tan <victortan@chromium.org>
Commit-Queue: Mike Taylor <miketaylr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1004251}

--

wpt-commits: 78ebac40dc10cfabd5b4f2afa076166689b86198
wpt-pr: 34080

testing/web-platform/tests/ua-client-hints/useragentdata.https.any.js

@@ -5,3 +5,10 @@ test(t => {
   assert_true(brands.every(brand => brand.brand.length < 32),
     "No brand should be longer than 32 characters.");
 });
+
+test(t => {
+  const uaData = navigator.userAgentData.toJSON();
+  assert_own_property(uaData, "brands", "toJSON() output has brands member");
+  assert_own_property(uaData, "mobile", "toJSON() output has mobile member");
+  assert_own_property(uaData, "platform", "toJSON() output has platform member");
+}, "test NavigatorUAData.toJSON() output");