TimelineTrackView hoisting refactor cl. Add access to the underlying model.
TimelineTrackView hoisting refactor cl. Add access to the underlying model.

Allow adding and removing annotations and getting the model's current bounds.
This is needed to allow TimelineTrackView to interact with the model through
the ModelTrack instead of directly.

BUG=catapult:#3126

Review-Url: https://codereview.chromium.org/2615353003

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