Added documentation for hls.xhr.beforeRequest with examples

@@ -19,6 +19,7 @@ Play back HLS with video.js, even where it's not natively supported.
     - [hls.bandwidth](#hlsbandwidth)
     - [hls.bandwidth](#hlsbandwidth)
     - [hls.bytesReceived](#hlsbytesreceived)
     - [hls.bytesReceived](#hlsbytesreceived)
     - [hls.selectPlaylist](#hlsselectplaylist)
     - [hls.selectPlaylist](#hlsselectplaylist)
+    - [hls.xhr](#hlsxhr)
   - [Events](#events)
   - [Events](#events)
     - [loadedmetadata](#loadedmetadata)
     - [loadedmetadata](#loadedmetadata)
     - [loadedplaylist](#loadedplaylist)
     - [loadedplaylist](#loadedplaylist)
@@ -194,6 +195,44 @@ segment is downloaded. You can override this function to provide your
 adaptive streaming logic. You must, however, be sure to return a valid
 adaptive streaming logic. You must, however, be sure to return a valid
 media playlist object that is present in `player.hls.master`.
 media playlist object that is present in `player.hls.master`.
 
 
+#### hls.xhr
+Type: `function`
+
+The xhr function that is used by HLS internally is exposed on the per-
+player `hls` object. While it is possible, we do not recommend replacing
+the function with your own implementation. Instead, the `xhr` provides
+the ability to specify a `beforeRequest` function that will be called
+with an object containing the options that will be used to create the
+xhr request.
+
+Example:
+```javascript
+player.hls.xhr.beforeRequest = function(options) {
+  options.uri = options.uri.replace('example.com', 'foo.com');
+
+  return options;
+};
+```
+
+The global `videojs.Hls` also exposes an `xhr` property. Specifying a
+`beforeRequest` function on that will allow you to intercept the options
+for *all* requests in every player on a page.
+
+Example
+```javascript
+videojs.Hls.xhr.beforeRequest = function(options) {
+  /*
+   * Modifications to requests that will affect every player.
+   */
+
+  return options;
+};
+```
+
+For information on the type of options that you can modify see the
+documentation at [https://github.com/Raynos/xhr](https://github.com/Raynos/xhr).
+
+
 ### Events
 ### Events
 Standard HTML video events are handled by video.js automatically and
 Standard HTML video events are handled by video.js automatically and
 are triggered on the player object. In addition, there are a couple
 are triggered on the player object. In addition, there are a couple

@@ -3366,17 +3366,15 @@ QUnit.test('selectPlaylist does not fail if getComputedStyle returns null', func
 QUnit.test('Allows specifying the beforeRequest functionon the player', function() {
 QUnit.test('Allows specifying the beforeRequest functionon the player', function() {
   let beforeRequestCalled = false;
   let beforeRequestCalled = false;
 
 
-  this.player.ready(function() {
-    this.hls.xhr.beforeRequest = function() {
-      beforeRequestCalled = true;
-    };
-  });
   this.player.src({
   this.player.src({
     src: 'master.m3u8',
     src: 'master.m3u8',
     type: 'application/vnd.apple.mpegurl'
     type: 'application/vnd.apple.mpegurl'
   });
   });
-
   openMediaSource(this.player, this.clock);
   openMediaSource(this.player, this.clock);
+
+  this.player.hls.xhr.beforeRequest = function() {
+    beforeRequestCalled = true;
+  };
   // master
   // master
   standardXHRResponse(this.requests.shift());
   standardXHRResponse(this.requests.shift());
   // media
   // media
@@ -3396,6 +3394,9 @@ QUnit.test('Allows specifying the beforeRequest function globally', function() {
     src: 'master.m3u8',
     src: 'master.m3u8',
     type: 'application/vnd.apple.mpegurl'
     type: 'application/vnd.apple.mpegurl'
   });
   });
+  openMediaSource(this.player, this.clock);
+  // master
+  standardXHRResponse(this.requests.shift());
 
 
   QUnit.ok(beforeRequestCalled, 'beforeRequest was called');
   QUnit.ok(beforeRequestCalled, 'beforeRequest was called');
 
 
@@ -3414,13 +3415,11 @@ QUnit.test('Allows overriding the global beforeRequest function', function() {
     src: 'master.m3u8',
     src: 'master.m3u8',
     type: 'application/vnd.apple.mpegurl'
     type: 'application/vnd.apple.mpegurl'
   });
   });
-  this.player.ready(function() {
-    this.hls.xhr.beforeRequest = function() {
+  openMediaSource(this.player, this.clock);
+
+  this.player.hls.xhr.beforeRequest = function() {
     beforeLocalRequestCalled++;
     beforeLocalRequestCalled++;
   };
   };
-  });
-
-  openMediaSource(this.player, this.clock);
   // master
   // master
   standardXHRResponse(this.requests.shift());
   standardXHRResponse(this.requests.shift());
   // media
   // media