Break up dependency cycle between search_engines and omnibox

In 2015 a dependency from search_engines to omnibox was created
and it's created a cycle that causes linking problems in some
ios+jumbo configurations. It works without jumbo because the cycle
will be part of a dead .o file which will be ignored by the linker.
With jumbo the .o file is not 100% dead anymore since dead and live
code will be mixed in it.

Bug: 488901
Change-Id: I4b36a1b4e9f46a2814d9562f288e55dadc63d9dd
Reviewed-on: https://chromium-review.googlesource.com/c/1254082
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597093}
6 files changed