Remove old Mojo JS bindings support in LayoutTests and WebUI

The old Mojo JS bindings are now only used in blessed extension
contexts. All of the support for LayoutTests and WebUI can be removed.
Logic to enable the new Mojo bindings in WebUI contexts is moved to
RenderFrameImpl::DidCreateScriptContext.

Bug: 699569
Change-Id: Ib0d9e43a6d73ada45a9286aa85e13d15bc421473
Reviewed-on: https://chromium-review.googlesource.com/706380
Reviewed-by: Charlie Reis <creis@chromium.org>
Reviewed-by: Nick Carter <nick@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509907}
25 files changed