Hide DevTools frontend from webRequest API

Prevent extensions from observing requests for remote DevTools frontends
and add regression tests.

And update ExtensionTestApi to support initializing the embedded test
server and port from SetUpCommandLine (before SetUpOnMainThread).

BUG=797497,797500
TEST=browser_test --gtest_filter=DevToolsFrontendInWebRequestApiTest.HiddenRequests
TBR=rob@robwu.nl

(cherry picked from commit 2649de11c562aa96d336c06136a1a20c01711be0)

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: Ic8f44b5771f2d5796f8c3de128f0a7ab88a77735
Reviewed-on: https://chromium-review.googlesource.com/844316
Commit-Queue: Rob Wu <rob@robwu.nl>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#528187}
Reviewed-on: https://chromium-review.googlesource.com/875984
Reviewed-by: Rob Wu <rob@robwu.nl>
Cr-Commit-Position: refs/branch-heads/3282@{#546}
Cr-Branched-From: 5fdc0fab22ce7efd32532ee989b223fa12f8171e-refs/heads/master@{#520840}
15 files changed