XMLHttpRequest: response header value containing 0x00

As discussed in whatwg/xhr#165 these should turn the response into a network error.

xhr/headers-normalize-response.htm

@@ -3,13 +3,15 @@
 <title>Whitespace and null in header values</title>
 <script src=/resources/testharness.js></script>
 <script src=/resources/testharnessreport.js></script>
-<script src=support.js?pipe=sub></script>
-
-<h1>Whitespace and null in response header values</h1>
-
 <div id=log></div>
-
 <script>
+function error(val) {
+  test(() => {
+    const client = new XMLHttpRequest();
+    client.open("GET", "resources/parse-headers.py?my-custom-header="+encodeURIComponent(val), false);
+    assert_throws("NetworkError", () => client.send());
+  }, "Header value: " + val.replace("\0", "\\0"));
+}
 
 function matchHeaderValue(val) {
     test(function () {
@@ -20,12 +22,12 @@ <h1>Whitespace and null in response header values</h1>
         var r = client.getResponseHeader("My-Custom-Header");
 
         assert_equals(r, trimmed);
-    }, "Header value: " + val.replace(/\t/g, "[tab]").replace(/ /g, "_").replace("\0", "\\0"));
+    }, "Header value: " + val.replace(/\t/g, "[tab]").replace(/ /g, "_"));
 }
 
-matchHeaderValue("hello world\0");
-matchHeaderValue("\0hello world");
-matchHeaderValue("hello\0world");
+error("hello world\0");
+error("\0hello world");
+error("hello\0world");
 matchHeaderValue("  hello world");
 matchHeaderValue("hello world  ");
 matchHeaderValue("  hello world  ");
@@ -34,9 +36,12 @@ <h1>Whitespace and null in response header values</h1>
 matchHeaderValue("\thello world\t");
 matchHeaderValue("hello      world");
 matchHeaderValue("hello\tworld");
-matchHeaderValue("\0");
+error("\0");
 matchHeaderValue("   ");
 matchHeaderValue("\t");
 matchHeaderValue("");
 
+promise_test(t => {
+  return promise_rejects(t, new TypeError(), fetch("resources/parse-headers.py?my-custom-header="+encodeURIComponent("x\0x")));
+}, "Ensure fetch() rejects too")
 </script>