Update Some StreamingEngine Tests to ES6
Update Some StreamingEngine Tests to ES6

In prep of doing some work with streaming engine, I needed to update
the test to use ES6 so that it will be easier to make the changes
needed in the tests to try out the ideas.

Issue #1157

Change-Id: I5b468a70a3514df07063c2aa3c56f1b265ce4cc6

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