[Fuchsia] Split navigation control and events out of FrameImpl.

NavigationControllerImpl holds all top-level frame navigation logic:
- Implementation of the fuchsia.web.NavigationController API.
- Logic to deliver updates to an attached NavigationEventListener.

Change-Id: I7f19de43cd17de0ad634c9218c7abe1dc6855053
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1672263
Reviewed-by: Kevin Marshall <[email protected]>
Commit-Queue: Wez <[email protected]>
Cr-Commit-Position: refs/heads/master@{#671951}
5 files changed