[Media Router] Add top-level js resources for Media Router UI.
The files added were:
media_router.js - contains handlers for UI events (e.g. user selected a
route) that manipulates the UI and uses the media_router_ui_interface.js
API.
media_router_ui_interface.js - API called by other js files, to
issue commands (e.g. create/close route) to C++ WebUI mesage handler.
Messages to manipulate the UI sent from C++ (e.g. update sink list) are
also received and handled here.
They are mostly empty implementations except for a few simple functions.
Added media_router.js and related js dependencies to media_router.html.
See crrev.com/
1115713004 for corresponding C++ patch.
BUG=464222
Review URL: https://codereview.chromium.org/
1113453008
Cr-Commit-Position: refs/heads/master@{#328010}