Omnibox: HQP - Allow Changing Number of Words in the Title to Match

Currently HistoryQuick provider has a fixed limit of considering 10
words in the title of a web page for matching.  This change makes
that limit controlled by a field trial.

BUG=291294

Review URL: https://codereview.chromium.org/1025833002

Cr-Commit-Position: refs/heads/master@{#321682}

chrome/browser/autocomplete/scored_history_match.cc

@@ -126,6 +126,7 @@ int ScoredHistoryMatch::bookmark_value_ = 1;
 bool ScoredHistoryMatch::fix_frequency_bugs_ = false;
 bool ScoredHistoryMatch::allow_tld_matches_ = false;
 bool ScoredHistoryMatch::allow_scheme_matches_ = false;
+size_t ScoredHistoryMatch::num_title_words_to_allow_ = 10u;
 bool ScoredHistoryMatch::hqp_experimental_scoring_enabled_ = false;
 float ScoredHistoryMatch::topicality_threshold_ = -1;
 std::vector<ScoredHistoryMatch::ScoreMaxRelevance>*
@@ -408,6 +409,7 @@ void ScoredHistoryMatch::Init() {
   fix_frequency_bugs_ = OmniboxFieldTrial::HQPFixFrequencyScoringBugs();
   allow_tld_matches_ = OmniboxFieldTrial::HQPAllowMatchInTLDValue();
   allow_scheme_matches_ = OmniboxFieldTrial::HQPAllowMatchInSchemeValue();
+  num_title_words_to_allow_ = OmniboxFieldTrial::HQPNumTitleWordsToAllow();
 
   InitRawTermScoreToTopicalityScoreArray();
   InitDaysAgoToRecencyScoreArray();
@@ -505,7 +507,7 @@ float ScoredHistoryMatch::GetTopicalityScore(
   // Now do the analogous loop over all matches in the title.
   next_word_starts = word_starts.title_word_starts_.begin();
   end_word_starts = word_starts.title_word_starts_.end();
-  int word_num = 0;
+  size_t word_num = 0;
   title_matches = FilterTermMatchesByWordStarts(
       title_matches, terms_to_word_starts_offsets,
       word_starts.title_word_starts_, 0, std::string::npos);
@@ -519,7 +521,7 @@ float ScoredHistoryMatch::GetTopicalityScore(
       ++next_word_starts;
       ++word_num;
     }
-    if (word_num >= 10)
+    if (word_num >= num_title_words_to_allow_)
       break;  // only count the first ten words
     DCHECK(next_word_starts != end_word_starts);
     DCHECK_EQ(*next_word_starts, title_match.offset + term_offset)

chrome/browser/autocomplete/scored_history_match.h

@@ -170,6 +170,10 @@ struct ScoredHistoryMatch : public history::HistoryMatch {
   // If true, we allow input terms to match in the scheme (e.g., "http://").
   static bool allow_scheme_matches_;
 
+  // The number of title words examined when computing topicality scores.
+  // Words beyond this number are ignored.
+  static size_t num_title_words_to_allow_;
+
   // True, if hqp experimental scoring is enabled.
   static bool hqp_experimental_scoring_enabled_;
 

components/omnibox/omnibox_field_trial.cc

@@ -378,6 +378,18 @@ bool OmniboxFieldTrial::HQPFixFrequencyScoringBugs() {
       kHQPFixFrequencyScoringBugsRule) == "true";
 }
 
+size_t OmniboxFieldTrial::HQPNumTitleWordsToAllow() {
+  // The value of the rule is a string that encodes an integer (actually
+  // size_t) containing the number of words.
+  size_t num_title_words;
+  if (!base::StringToSizeT(
+          variations::GetVariationParamValue(kBundledExperimentFieldTrialName,
+                                             kHQPNumTitleWordsRule),
+          &num_title_words))
+    return 10;
+  return num_title_words;
+}
+
 const char OmniboxFieldTrial::kBundledExperimentFieldTrialName[] =
     "OmniboxBundledExperimentV1";
 const char OmniboxFieldTrial::kDisableProvidersRule[] = "DisableProviders";
@@ -404,6 +416,7 @@ const char OmniboxFieldTrial::kSuggestPollingDelayMsRule[] =
     "SuggestPollingDelayMs";
 const char OmniboxFieldTrial::kHQPFixFrequencyScoringBugsRule[] =
     "HQPFixFrequencyScoringBugs";
+const char OmniboxFieldTrial::kHQPNumTitleWordsRule[] = "HQPNumTitleWords";
 
 const char OmniboxFieldTrial::kHUPNewScoringEnabledParam[] =
     "HUPExperimentalScoringEnabled";

components/omnibox/omnibox_field_trial.h

@@ -299,6 +299,15 @@ class OmniboxFieldTrial {
   // function.
   static bool HQPFixFrequencyScoringBugs();
 
+  // ---------------------------------------------------------
+  // For the HQPNumTitleWords experiment that's part of the
+  // bundled omnibox field trial.
+
+  // Returns the number of title words that are allowed to contribute
+  // to the topicality score.  Words later in the title are ignored.
+  // Returns 10 as a default if the experiment isn't active.
+  static size_t HQPNumTitleWordsToAllow();
+
   // ---------------------------------------------------------
   // Exposed publicly for the sake of unittests.
   static const char kBundledExperimentFieldTrialName[];
@@ -319,6 +328,7 @@ class OmniboxFieldTrial {
   static const char kMeasureSuggestPollingDelayFromLastKeystrokeRule[];
   static const char kSuggestPollingDelayMsRule[];
   static const char kHQPFixFrequencyScoringBugsRule[];
+  static const char kHQPNumTitleWordsRule[];
 
   // Parameter names used by the HUP new scoring experiments.
   static const char kHUPNewScoringEnabledParam[];