[3/3 blink] Support redirect option of Request and "opaqueredirect" response type.

LayoutTests/http/tests/serviceworker/resources/fetch-request-redirect-iframe.html

 <script>
 function xhr(url) {
   return new Promise(function(resolve, reject) {
       var request = new XMLHttpRequest();
       request.addEventListener(
         'error',
         function(event) { reject(event); });
       request.addEventListener(
         'load',
         function(event) { resolve(request.response); });
       request.open('GET', url);
       request.send();
     });
 }
 
-function load_image(url, cross_origin) {
+function load_image(url) {
   return new Promise(function(resolve, reject) {
       var img = document.createElement('img');
       document.body.appendChild(img);
-      img.onload = function() {
-        resolve();
-      };
-      img.onerror = function() {
-        reject();
-      };
-      if (cross_origin != '') {
-        img.crossOrigin = cross_origin;
-      }
+      img.onload = resolve;
+      img.onerror = reject;
       img.src = url;
     });
 }
+
+function load_audio(url) {
+  return new Promise(function(resolve, reject) {
+      var audio = document.createElement('audio');
+      document.body.appendChild(audio);
+      audio.oncanplay = resolve;
+      audio.onerror = reject;
+      audio.src = url;
+    });
+}
 </script>