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This infrastructure will hopefully form the basis of the state
management for the borealis system. The important concepts are:
 - State is managed by manager objects, which can be in exactly two
   states (on/off)
 - State is conceptualized with state objects, that are constructed or
   destroyed during state transitions, based on what those transitions
   are defined as.
 - The state manager owns the instance of the state object, so we force
   designs that work a bit like an onion/stack in the sense that
   if state C is a descendant of P then we model this by having P own
   the *state manager* for C (as opposed to having C own/inherit/extend
   P itself).

Bug: b/172178036
Change-Id: I2b065f71972d11e3212509f2f4c569e598ca9c41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526865Reviewed-by: David Munro <davidmunro@google.com>
Reviewed-by: Daniel Ng <danielng@google.com>
Commit-Queue: Nic Hollingum <hollingum@google.com>
Cr-Commit-Position: refs/heads/master@{#830784}