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This commit is part 1 of 2, being a refactor with no change in behavior.
There is an existing observer leak (an AddObserver call with no matching
RemoveObserver call), but this commit keeps that leak. A follow-up
commit will fix the leak.

TBR=seantopping@chromium.org

Change-Id: I73e9087540949c29bb76d6526362b5448452e182
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585403
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Reviewed-by: Sean Topping <seantopping@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654688}