Rather than test for fetch, limit the code to ES6 browsers.
Depends-On: I96a03796628a74ace93579d45a582711400c09c1
Change-Id: I4ca10182491118e61e155f99c713d4cb1b4fc7f0
This will allow us to write ES6 code for the new features which
is limited to those browsers.
For browsers that do not support ES6, the code will not execute
because of the "es6" flag. Doing this will help us avoid issues
like T293402
Change-Id: Iffb7098cb22395e33b87352fb4f08516f6f25e6f