Fix race in Player WRT external text tracks.

When adding text tracks, the Player did not add the stream to the
manifest until after it is initialized.  However, the streaming
engine may schedule an update before the track is added causing it
to fail.  Now the Player will add the stream first.

Closes #418

Change-Id: I4758aabcddfb69bc54b805351c22df7516a57b2e

lib/player.js

@@ -110,6 +110,9 @@ shaka.Player = function(video, opt_dependencyInjector) {
    */
   this.nextExternalStreamId_ = 1e9;
 
+  /** @private {!Array.<number>} */
+  this.loadingTextStreamIds_ = [];
+
   /** @private {boolean} */
   this.buffering_ = false;
 
@@ -799,7 +802,11 @@ shaka.Player.prototype.getTracks = function() {
 
   var activeStreams = this.streamingEngine_.getActiveStreams();
   var period = this.streamingEngine_.getCurrentPeriod();
-  return shaka.util.StreamUtils.getTracks(period, activeStreams);
+  return shaka.util.StreamUtils.getTracks(period, activeStreams)
+      .filter(function(track) {
+        // Don't show any tracks that are being loaded still.
+        return this.loadingTextStreamIds_.indexOf(track.id) < 0;
+      }.bind(this));
 };
 
 
@@ -984,12 +991,17 @@ shaka.Player.prototype.addTextTrack = function(
     streams: [stream]
   };
 
+  // Add the stream to the loading list to ensure it isn't switched to while it
+  // is initializing.
+  this.loadingTextStreamIds_.push(stream.id);
+  period.streamSets.push(streamSet);
+
   return this.streamingEngine_.notifyNewStream('text', stream).then(function() {
     if (this.destroyed_) return;
 
-    // Only add the stream once it has been initialized.  This ensures that
-    // calls to getTracks do not return the uninitialized stream.
-    period.streamSets.push(streamSet);
+    // Remove the stream from the loading list.
+    this.loadingTextStreamIds_.splice(
+        this.loadingTextStreamIds_.indexOf(stream.id), 1);
 
     // This will disable AbrManager but it will be enabled again below.
     var chosen = this.chooseStreams_(period);