Change behaivor to decide whether a search engine should be shown in the default list
1. Delete show_in_default_list field in template_url_data.
2. New rule checks whether a search engine is prepopulated or created by
policy or now selected as default to decide whether it should appears in the
default search setting list. The search engine should also support search
term replacement if it is in that list.
3. Search engines parsed from Firefox by default will not appears in the
default list.
BUG=348360
Review-Url: https://codereview.chromium.org/2487633003
Cr-Commit-Position: refs/heads/master@{#433151}
32 files changed
