Fix snapback feature on DAI streams.
Fix snapback feature on DAI streams.

If a user seeks past an ad break in the SS DAI stream,
they are returned to the start of an ad break and then
to the point of their original seek, after the ad played
through.

Issue #2367.

Change-Id: I2205f76911439cabb7d55a57b7aa0b163d65efc8

shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player