Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/resources/utils.js

+var inWorker = false;
+var RESOURCES_DIR = "../resources/";
+
+try {
+  inWorker = !(self instanceof Window);
+} catch (e) {
+  inWorker = true;
+}
+
+function dirname(path) {
+    return path.replace(/\/[^\/]*$/, '/')
+}
+
+function checkRequest(request, ExpectedValuesDict) {
+  for (var attribute in ExpectedValuesDict) {
+    switch(attribute) {
+      case "headers":
+        for (var key in ExpectedValuesDict["headers"].keys()) {
+          assert_equals(request["headers"].get(key), ExpectedValuesDict["headers"].get(key),
+            "Check headers attribute has " + key + ":" + ExpectedValuesDict["headers"].get(key));
+        }
+        break;
+
+      case "body":
+        //for checking body's content, a dedicated asyncronous/promise test should be used
+        assert_true(request["headers"].has("Content-Type") , "Check request has body using Content-Type header")
+        break;
+
+      case "method":
+      case "referrer":
+      case "referrerPolicy":
+      case "credentials":
+      case "cache":
+      case "redirect":
+      case "integrity":
+      case "url":
+      case "destination":
+        assert_equals(request[attribute], ExpectedValuesDict[attribute], "Check " + attribute + " attribute")
+        break;
+
+      default:
+        break;
+    }
+  }
+}
+
+function stringToArray(str) {
+  var array = new Uint8Array(str.length);
+  for (var i=0, strLen = str.length; i < strLen; i++)
+    array[i] = str.charCodeAt(i);
+  return array;
+}
+
+function encode_utf8(str)
+{
+    if (self.TextEncoder)
+        return (new TextEncoder).encode(str);
+    return stringToArray(unescape(encodeURIComponent(str)));
+}
+
+function validateBufferFromString(buffer, expectedValue, message)
+{
+  return assert_array_equals(new Uint8Array(buffer !== undefined ? buffer : []), stringToArray(expectedValue), message);
+}
+
+function validateStreamFromString(reader, expectedValue, retrievedArrayBuffer) {
+  return reader.read().then(function(data) {
+    if (!data.done) {
+      assert_true(data.value instanceof Uint8Array, "Fetch ReadableStream chunks should be Uint8Array");
+      var newBuffer;
+      if (retrievedArrayBuffer) {
+        newBuffer =  new ArrayBuffer(data.value.length + retrievedArrayBuffer.length);
+        newBuffer.set(retrievedArrayBuffer, 0);
+        newBuffer.set(data.value, retrievedArrayBuffer.length);
+      } else {
+        newBuffer = data.value;
+      }
+      return validateStreamFromString(reader, expectedValue, newBuffer);
+    }
+    validateBufferFromString(retrievedArrayBuffer, expectedValue, "Retrieve and verify stream");
+  });
+}
+
+// From streams tests
+function delay(milliseconds)
+{
+  return new Promise(function(resolve) {
+    step_timeout(resolve, milliseconds);
+  });
+}