Don't gap jump until seeking event fires

This changes onPollGapJump_ to not gap jump if the video is seeking
but a seeking event has not yet occurred.
This also adds a unit test that tests for the bug in issue shaka-project#1061.

Closes shaka-project#1061

Change-Id: I8662f5878006ed8626ca8df55f0506edb2dd970e

lib/media/playhead.js

@@ -90,6 +90,9 @@ shaka.media.Playhead = function(
   /** @private {?shaka.util.Timer} */
   this.gapJumpTimer_ = null;
 
+  /** @private {boolean} */
+  this.seekingEventReceived_ = false;
+
   /**
    * Used to batch up early seeks and delay until video.currentTime is updated.
    *
@@ -422,6 +425,14 @@ shaka.media.Playhead.prototype.onSeekingToStartTime_ = function() {
 shaka.media.Playhead.prototype.onPollGapJump_ = function() {
   // Don't gap jump before the video is ready to play.
   if (this.video_.readyState == 0) return;
+  // Do not gap jump if seeking has begun, but the seeking event has not
+  // yet fired for this particular seek.
+  if (this.video_.seeking) {
+    if (!this.seekingEventReceived_)
+      return;
+  } else {
+    this.seekingEventReceived_ = false;
+  }
   // Don't gap jump while paused, so that you don't constantly jump ahead while
   // paused on a livestream.
   if (this.video_.paused) return;
@@ -563,6 +574,7 @@ shaka.media.Playhead.prototype.onSeeking_ = function() {
   goog.asserts.assert(this.video_.readyState > 0,
                       'readyState should be greater than 0');
 
+  this.seekingEventReceived_ = true;
   this.hadSegmentAppended_ = false;
   var currentTime = this.video_.currentTime;
   var targetTime = this.reposition_(currentTime);

test/media/playhead_unit.js

@@ -1013,6 +1013,34 @@ describe('Playhead', function() {
       });  // with large gaps
     });  // with unbuffered seeks
 
+    it('doesn\'t gap jump if the seeking event is late', function() {
+      var buffered = [{start: 10, end: 20}];
+      video.buffered = createFakeBuffered(buffered);
+      video.currentTime = 12;
+      video.readyState = HTMLMediaElement.HAVE_ENOUGH_DATA;
+
+      config.jumpLargeGaps = true;
+      playhead = new shaka.media.Playhead(video, manifest, config, 12,
+                                          Util.spyFunc(onSeek),
+                                          Util.spyFunc(onEvent));
+
+      jasmine.clock().tick(1000);
+      expect(onEvent).not.toHaveBeenCalled();
+
+      // Append a segment before seeking.
+      playhead.onSegmentAppended();
+
+      // Seek backwards but wait briefly to fire the seeking event.
+      video.currentTime = 3;
+      video.readyState = HTMLMediaElement.HAVE_METADATA;
+      video.seeking = true;
+      jasmine.clock().tick(600);
+      video.on['seeking']();
+
+      // There should NOT have been a gap jump.
+      expect(video.currentTime).toBe(3);
+    });
+
     /**
      * @param {string} name
      * @param {SeekTestInfo} data