Move web Runner implementation to //webrunner/app/{web,common}.

- Expose WebContentRunner's constructor to derived classes.
- Move the common Runner and Component implementations under "common".
- Move the scoped service publishing binding into WebContentRunner.
- Move the default web.Context creation helper to the WebContentRunner.
- Rename the ComponentControllerImpl to WebComponent.
- Rename WebComponent::RequestTermination to ...::DestroyComponent.

Bug: 893229, 856416
Change-Id: Ia4b8036d5f1b6f00472d201b7cb9dcf063377122
Reviewed-on: https://chromium-review.googlesource.com/c/1301114
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604002}
12 files changed