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To debug tests, they need to be executed with the following switches:
--remote-debugging-port=9222
--enable-file-manager-step-by-step-tests
--enable-pixel-output-in-tests
--ui-test-action-timeout=10000000

Then run http://localhost:9222 in a separate browser window, then select
"chrome manager browser tests" and follow instructions.

TEST=Tested manually.
BUG=460813

Review URL: https://codereview.chromium.org/942393002

Cr-Commit-Position: refs/heads/master@{#317559}