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It's a part of larger task to move the whole initialization
on the separate thread. Previous CL introduced some hard to
track issues and broke some perf bots. This CL is first part
to make sure bots are fine. It moves gconf related
initialization on the file thread.

BUG=472183, 468989, 468112

Review URL: https://codereview.chromium.org/1640273002

Cr-Commit-Position: refs/heads/master@{#372074}