Move networking_private to src/extensions

The major re-factoring for this has been done, this is mostly just
moving the files, with a small addition to ExtensionsBrowserClient.

For extensions/browser/api/networking_private/DEPS:
[email protected]
BUG=363776

Review URL: https://codereview.chromium.org/870163002

Cr-Commit-Position: refs/heads/master@{#313537}
52 files changed