[local-search-service] Disable partial match for token set ratio

TokenSetRatio calculates pairwise string match ratios between the
following three and returns the max as the final result.
(i). intersection string (of query & text)
(ii). query rewritten (intersection + query_diff_text)
(iii). text rewritten (intersection + text_diff_query)

If we enable partial match, then (i) and (ii) or (i) and (iii)
will return extremely high ratios (close to 1) if intersection
is non-empty. This means if there is any common word between
query and text, the result ratio will be too high.

This cl disables partial match in TokenSetRatio.

Bug: 1081584
Change-Id: If4062c367f74be62a733d6b0e3d54353bfba1365
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2206057Reviewed-by: Thanh Nguyen <thanhdng@chromium.org>
Commit-Queue: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769626}

chrome/common/string_matching/fuzzy_tokenized_string_match.cc

@@ -253,9 +253,13 @@ double FuzzyTokenizedStringMatch::WeightedRatio(
                TokenSortRatio(query, text, use_partial /*partial*/,
                               partial_match_penalty_rate, use_edit_distance) *
                    unbase_scale * partial_scale);
+
+  // Do not use partial match for token set because the match between the
+  // intersection string and query/text rewrites will always return an extremely
+  // high value.
   weighted_ratio =
       std::max(weighted_ratio,
-               TokenSetRatio(query, text, use_partial /*partial*/,
+               TokenSetRatio(query, text, false /*partial*/,
                              partial_match_penalty_rate, use_edit_distance) *
                    unbase_scale * partial_scale);
   return weighted_ratio;

chrome/common/string_matching/fuzzy_tokenized_string_match_unittest.cc

@@ -161,7 +161,7 @@ TEST_F(FuzzyTokenizedStringMatchTest, WeightedRatio) {
     EXPECT_NEAR(
         match.WeightedRatio(TokenizedString(query), TokenizedString(text),
                             kPartialMatchPenaltyRate, false),
-        0.85, 0.01);
+        0.49, 0.01);
   }
 }