Add a reference to bug tracking componentization of search_engines tests.
Add a reference to bug tracking componentization of search_engines tests.

BUG=527882

Review URL: https://codereview.chromium.org/1315303008

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347368}

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