Extensions: convert media_router_bindings.js to use new Mojo JS bindings.

This CL also changes the mojoPrivate API to be simply an async wrapper around
require().

Bug: 699569, 718047
Change-Id: I271887d1cc1eb49fd2faefff47467c47be23a3be
Reviewed-on: https://chromium-review.googlesource.com/783645
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Derek Cheng <imcheng@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Yuzhu Shen <yzshen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521129}
11 files changed