Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/basic/scheme-about.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("../resources/utils.js");
+}
+
+function checkFetchResponse(url, method, desc) {
+  if (!desc) {
+    var cut = (url.length >= 40) ? "[...]" : "";
+    cut += " (" + method + ")"
+    desc = "Fetching " + url.substring(0, 40) + cut + " is OK"
+  }
+  promise_test(function(test) {
+    return fetch(url, { method: method }).then(function(resp) {
+     assert_equals(resp.status, 200, "HTTP status is 200");
+     assert_equals(resp.type, "basic", "response type is basic");
+     assert_equals(resp.headers.get("Content-Type"), "text/html;charset=utf-8", "Content-Type is " + resp.headers.get("Content-Type"));
+     return resp.text();
+    })
+  }, desc);
+}
+
+checkFetchResponse("about:blank", "GET");
+checkFetchResponse("about:blank", "PUT");
+checkFetchResponse("about:blank", "POST");
+
+function checkKoUrl(url, desc) {
+  if (!desc)
+    desc = "Fetching " + url.substring(0, 45) + " is KO"
+  promise_test(function(test) {
+    var promise = fetch(url);
+    return promise_rejects(test, new TypeError(), promise);
+  }, desc);
+}
+
+checkKoUrl("about:invalid.com");
+checkKoUrl("about:config");
+checkKoUrl("about:unicorn");
+
+done();