[iOS] Add chrome://inspect webUI page.

Remove the Debug only "Log JS" switch from the Settings page.

Add a new chrome://inspect webUI page with a button to enable and
disable JavaScript console logging. Messages are still logged in the
same manner to the Xcode console, but will be moved to be displayed on
the chrome://inspect page in a follow-up CL.

The new UI of the chrome://inspect page can be seen here:

Bug: 899851
Change-Id: I653c1e31f95cf15d5acfe453d92c56f5e5e0431e
Reviewed-on: https://chromium-review.googlesource.com/c/1363632
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Mike Dougherty <michaeldo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616736}
15 files changed