- Introduce NodeSpace that holds allocation related logic.
- Provide std compatible iterator for node iteration.

This allows for creating a different internal node type.

The change is just a refactoring without functional changes.

Bug: chromium:923361
Change-Id: I424f821d96b3a82f64024aedff6c289d3eec11a2
Reviewed-on: https://chromium-review.googlesource.com/c/1418192
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58931}