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The tests were timing out because they would bring up the first
run dialog, which blocks user input and prevents the tests from
continuing.

This CL fixes the tests by suppressing the first run dialog for
the master prefs using a new ForTesting API. Also removes the
kForceFirstRunDialog command-line in favor of the new testing API.

Also cleans up some namespaces in the test code.

Bug: 314221, 910059
Change-Id: I3a366e49c9a115747fe42848146c81c5df8fffee
Reviewed-on: https://chromium-review.googlesource.com/c/1372427
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616109}