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This CL exposes a method that allows the creation of FileURLLoaderFactory
instances. through the content/browser public API.

This is a preparation for CL https://crrev.com/c/1066370.

BUG=773295,844928

Change-Id: I89c9cd2e82ee54f4dae1c121d5e0f7b5c0597fb1
Reviewed-on: https://chromium-review.googlesource.com/1156885
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579818}