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This is the core of the Commander.

It:
- Receives input from the UI and responds with view models
- Handles coordinating multiple sources of commands
- Sorts and filters results
- Serves as an intermediary between the view and a secondary
  backend if a composite command is being entered

Bug: 1014639

Change-Id: Ife8022e5e5471cbe6dc794823f7acf1de7023d40
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2304970Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792860}