Seek after clearing a buffer. Workaround for a Chrome bug.

A bug in Chrome makes video feed freeze for a while after a buffer
is cleared. Seeking helps to avoid freezing.
A bug on Chrome: http://crbug.com/651904

Change-Id: I80d9139cb02e859d9a0165235c9868d9afa8adfa

lib/media/playhead.js

@@ -348,7 +348,7 @@ shaka.media.Playhead.prototype.onSeeking_ = function() {
   var targetTime = this.reposition_(currentTime);
 
   if (Math.abs(targetTime - currentTime) > 0.001) {
-    this.movePlayhead_(currentTime, targetTime);
+    this.movePlayhead(currentTime, targetTime);
     return;
   }
 
@@ -370,7 +370,7 @@ shaka.media.Playhead.prototype.onPlaying_ = function() {
   var targetTime = this.reposition_(currentTime);
 
   if (Math.abs(targetTime - currentTime) > 0.001)
-    this.movePlayhead_(currentTime, targetTime);
+    this.movePlayhead(currentTime, targetTime);
 };
 
 
@@ -440,9 +440,8 @@ shaka.media.Playhead.prototype.reposition_ = function(currentTime) {
  *
  * @param {number} currentTime
  * @param {number} targetTime
- * @private
  */
-shaka.media.Playhead.prototype.movePlayhead_ = function(
+shaka.media.Playhead.prototype.movePlayhead = function(
     currentTime, targetTime) {
   shaka.log.debug('Moving playhead...',
                   'currentTime=' + currentTime,

lib/media/streaming_engine.js

@@ -1715,6 +1715,17 @@ shaka.media.StreamingEngine.prototype.clearBuffer_ = function(
     mediaState.lastSegmentReference = null;
     mediaState.clearingBuffer = false;
     this.scheduleUpdate_(mediaState, 0);
+
+    // A workaround for a chrome bug: http://crbug.com/651904
+    // Video freezes for a while after buffer is cleared.
+    // Advancing the playhead a little allows to avoid the freeze.
+    // NOTE: Opera has the same issue as it is based on Chrome.
+    // It also returns true on window.chrome and will unfreeze
+    // after seeking.
+    if (window.chrome) {
+      var currentTime = this.playhead_.getTime();
+      this.playhead_.movePlayhead(currentTime, currentTime + 0.1);
+    }
   }.bind(this));
 };