[Compare] Only show results if Google is default search engine

This patch adds the TemplateURLService as a dependency to the
shopping service to allow us to internally check the default
search engine. Comparison data can only be loaded if the search
engine is Google. A test has been added for this new case.

Bug: 374157577
Change-Id: Ifdec7d310477b3cf7e2fb144f8664e7c5bb154ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5941576
Reviewed-by: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Ayman Almadhoun <ayman@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1372771}