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This CL starts the effort to move dependencies of the service into
dedicated classes in order to facilitate unit testing and code reuse.

This CL is a refactoring only and should have no user-facing changes.
I plan to add dedicated unit tests in a follow-up.

Bug: b/158998456
Change-Id: Icd468ff98d9e1f5a028282b0e1eb42364aa46d16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2448496
Commit-Queue: Clemens Arbesser <arbesser@google.com>
Reviewed-by: Sandro Maggi <sandromaggi@google.com>
Cr-Commit-Position: refs/heads/master@{#814179}