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This is a small refactor CL that sets the ground work for enabling
conncurent URL Loaders.

There is no behavior change.

Bug: 1110962
Change-Id: I98c54048be9319378b3b3da1c81061e4b4a95ee2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327011Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792802}