Pull out XHR helper

Create a helper method for creating XMLHttpRequests and migrate downloadPlaylist to using it.

@@ -94,6 +94,35 @@ var
     }
   },
 
+  xhr = function(url, callback) {
+    var
+      options = {
+        method: 'GET'
+      },
+      request;
+    if (typeof url === 'object') {
+      options = videojs.util.mergeOptions(options, url);
+      url = options.url;
+    }
+    request = new window.XMLHttpRequest();
+    request.open(options.method, url);
+    request.onreadystatechange = function() {
+      // wait until the request completes
+      if (this.readyState !== 4) {
+        return;
+      }
+
+      // request error
+      if (this.status >= 400 || this.status === 0) {
+        return callback.call(this, true, url);
+      }
+
+      return callback.call(this, false, url);
+    };
+    request.send(null);
+    return request;
+  },
+
   /**
    * TODO - Document this great feature.
    *
@@ -350,7 +379,7 @@ var
       if (!playlist.segments ||
           mediaSequence < (playlist.mediaSequence || 0) ||
           mediaSequence > (playlist.mediaSequence || 0) + playlist.segments.length) {
-        downloadPlaylist(resolveUrl(srcUrl, playlist.uri));
+        xhr(resolveUrl(srcUrl, playlist.uri), downloadPlaylist);
       } else {
         player.hls.mediaIndex =
           findCorrespondingMediaIndex(player.hls.mediaIndex,
@@ -437,32 +466,26 @@ var
     };
 
     /**
-     * Download an M3U8 and update the current manifest object. If the provided
-     * URL is a master playlist, the default variant will be downloaded and
-     * parsed as well. Triggers `loadedmanifest` once for each playlist that is
-     * downloaded and `loadedmetadata` after at least one media playlist has
-     * been parsed. Whether multiple playlists were downloaded or not, when
-     * `loadedmetadata` fires a parsed or inferred master playlist object will
-     * be available as `player.hls.master`.
+     * Callback that is invoked when a playlist finishes
+     * downloading. If the response is a master playlist, the default
+     * variant will be downloaded and parsed as well. Triggers
+     * `loadedmanifest` once for each playlist that is downloaded and
+     * `loadedmetadata` after at least one media playlist has been
+     * parsed. Whether multiple playlists were downloaded or not, when
+     * `loadedmetadata` fires a parsed or inferred master playlist
+     * object will be available as `player.hls.master`.
      *
+     * @param error {*} truthy if the request was not successful
      * @param url {string} a URL to the M3U8 file to process
      */
-    downloadPlaylist = function(url) {
-      var xhr = new window.XMLHttpRequest();
-      xhr.open('GET', url);
-      xhr.onreadystatechange = function() {
+    downloadPlaylist = function(error, url) {
       var i, parser, playlist, playlistUri, refreshDelay;
 
-        // wait until the request completes
-        if (xhr.readyState !== 4) {
-          return;
-        }
-
-        if (xhr.status >= 400 || this.status === 0) {
+      if (error) {
         player.hls.error = {
-            status: xhr.status,
+          status: this.status,
           message: 'HLS playlist request error at URL: ' + url,
-            code: (xhr.status >= 500) ? 4 : 2
+          code: (this.status >= 500) ? 4 : 2
         };
         player.trigger('error');
         return;
@@ -470,12 +493,12 @@ var
 
       // readystate DONE
       parser = new videojs.m3u8.Parser();
-        parser.push(xhr.responseText);
+      parser.push(this.responseText);
 
       // master playlists
       if (parser.manifest.playlists) {
         player.hls.master = parser.manifest;
-          downloadPlaylist(resolveUrl(url, parser.manifest.playlists[0].uri));
+        xhr(resolveUrl(url, parser.manifest.playlists[0].uri), downloadPlaylist);
         player.trigger('loadedmanifest');
         return;
       }
@@ -525,7 +548,7 @@ var
       // check the playlist for updates if EXT-X-ENDLIST isn't present
       if (!parser.manifest.endList) {
         window.setTimeout(function() {
-            downloadPlaylist(url);
+          xhr(url, downloadPlaylist);
         }, refreshDelay);
       }
 
@@ -550,8 +573,6 @@ var
 
       player.trigger('loadedmanifest');
     };
-      xhr.send(null);
-    };
 
     /**
      * Determines whether there is enough video data currently in the buffer
@@ -668,7 +689,7 @@ var
       sourceBuffer.appendBuffer(segmentParser.getFlvHeader());
 
       player.hls.mediaIndex = 0;
-      downloadPlaylist(srcUrl);
+      xhr(srcUrl, downloadPlaylist);
     });
     player.src([{
       src: videojs.URL.createObjectURL(mediaSource),