The Chromium test DialogDoesNotShowWithExtensionEnabledThatOverridesDSE
fails on Linux because ApplyDefaultSearchChangeForTesting(FROM_EXTENSION)
leaves default_search_provider_ null (extension DSEs are unsupported on
Linux) while default_search_provider_source_ stays FROM_EXTENSION.
Brave's DefaultSearchManager override causes MaybeShowDialog() to record
the Search.ChoiceScreenNavigationConditions histogram twice with
differing conditions (kControlledByPolicy and kExtensionControlled),
failing the ExpectUniqueSample assertion.
Already disabled on Windows in upstream source. Upstream TODO
crbug.com/429600559 acknowledges the broken extension DSE test setup.
Stable upstream (0.3% flake rate over 30 days per LUCI Analysis).
Resolves https://github.com/brave/brave-browser/issues/54542
Netzenbot
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