GitLab

This CL:
* Converts network_ui.html/js to a Polymer element
* Introduces a browser proxy for chrome.send / cr.sendWithPromise calls
* Replaces chrome.send + listeners with cr.sendWithPromise
* Replaces cr tabpanels with cr-tabs + iron-pages.

Bug: 921726
Change-Id: Ib140fc17de7b000205709dfee619b848c56448a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2265503Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#782594}