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In particular, make HistoryURL provider scoring
basically the same within regular mode and
prevent-inline-autocomplete mode (under the constraint
that we always need a valid default match first).
For what it's worth, the current code demotes (from
~1410) all non-URL-what-you-typed URLs (non-UWYT)
to 900 in prevent-inline-autocomplete mode.  If
there is a UWYT, though, these results will be
clustered / given a free ride to appear right
below it, scoring ~1200.  After this change, all
non-UWYT results will score the same in
prevent-inline-autocomplete and normal modes.
We instead rely on the allowed_to_be_default_match
bit to reorder results as necessary.

To implement this feature, we need knowledge of
whether the what-you-typed match is reasonable.
This change re-adds a variable
have_what_you_typed_match to HistoryURLParams.  This
variable was previously added in
https://codereview.chromium.org/347963002 for
a field trial and then later removed in
https://codereview.chromium.org/879053002

With this variable, the change is straightforward.
Don't change the scoring in prevent-inline-autocomplete
mode.  Instead, simply make sure the what-you-type
match gets added to the list in prevent-inline-mode.
We add it early on the list (using the Promote()
mechanism) so that it'll always appear in the final
set of suggestions.

Tested using about:omnibox

BUG=421772

Review URL: https://codereview.chromium.org/1022643002

Cr-Commit-Position: refs/heads/master@{#322528}