Adding hard-coded minBufferTime to offline playback. Issue #22.

minBufferTime is hard-coded when reconstructing manifestInfo
from offline. This is needed to prevent failing assertions
during playback. 5 was chosen because it is large enough to
keep playback going properly and small enough that the buffered
data won't get garbage collected.

Change-Id: Iabb08137bda95d15f35a5e5f6386c0be321de7fa

lib/player/offline_video_source.js

@@ -361,6 +361,7 @@ shaka.player.OfflineVideoSource.prototype.load = function(preferredLanguage) {
 shaka.player.OfflineVideoSource.prototype.reconstructManifestInfo_ =
     function(indexes, duration, keySystem) {
   var manifestInfo = new shaka.media.ManifestInfo();
+  manifestInfo.minBufferTime = 5;
   // TODO(story 1890046): Support multiple periods.
   var periodInfo = new shaka.media.PeriodInfo();