[WPT] Add a test for fetch + non-ascii request header values

Note: although the test case originates from crbug.com/1119729,
this is NOT a regression test for crbug.com/1119729
that turned to be a DevTools issue (not a Fetch API issue).

Bug: 1119729
Change-Id: Ica0a9d0c91314bf6ba54f3f73cb9f77cc0e94915
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367580Reviewed-by: Yoichi Osato <yoichio@chromium.org>
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805223}

third_party/blink/web_tests/external/wpt/fetch/api/basic/request-headers-nonascii.any.js

+// This tests characters that are not
+// https://infra.spec.whatwg.org/#ascii-code-point
+// but are still
+// https://infra.spec.whatwg.org/#byte-value
+// in request header values.
+// Such request header values are valid and thus sent to servers.
+// Characters outside the #byte-value range are tested e.g. in
+// fetch/api/headers/headers-errors.html.
+
+promise_test(() => {
+  return fetch(
+    "../resources/inspect-headers.py?headers=accept|x-test",
+    {headers: {
+      "Accept": "before-æøå-after",
+      "X-Test": "before-ß-after"
+    }})
+    .then(res => {
+      assert_equals(
+          res.headers.get("x-request-accept"),
+          "before-æøå-after",
+          "Accept Header");
+      assert_equals(
+          res.headers.get("x-request-x-test"),
+          "before-ß-after",
+          "X-Test Header");
+    });
+}, "Non-ascii bytes in request headers");