a11y inspect reorg: move tests required command line setup out of tree
formatter

Keep tree formatters generic: command line setup is used for testing
only and thus the logic should be moved to where appropriate.
DumpTestHelper class already handles all test related logic,
thus move command line setup logic there

Bug: 1133330
Change-Id: I330788c1b263447f4882f92dbce5c62581a6352e
AX-Relnotes: n/a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2533905
Commit-Queue: Alexander Surkov <asurkov@igalia.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827366}