Add confidence to AutocompleteMatch.

chrome/browser/autocomplete/history_quick_provider.h

Index: chrome/browser/autocomplete/history_quick_provider.h
diff --git a/chrome/browser/autocomplete/history_quick_provider.h b/chrome/browser/autocomplete/history_quick_provider.h
index bd7a8244acba8d84250f0083e1d5c278ef5ed19c..a77c34396c4e89eda52674783b40b9bc551784fb 100644
--- a/chrome/browser/autocomplete/history_quick_provider.h
+++ b/chrome/browser/autocomplete/history_quick_provider.h
@@ -49,9 +49,11 @@ class HistoryQuickProvider : public HistoryProvider {
   static const int kMaxNonInliningScore;
 
   // Creates an AutocompleteMatch from |history_match|. |max_match_score| gives
-  // the maximum possible score for the match.
+  // the maximum possible score for the match. |history_matches| is the full set
+  // of matches to compare each match to when calculating confidence.
   AutocompleteMatch QuickMatchToACMatch(
       const history::ScoredHistoryMatch& history_match,
+      const history::ScoredHistoryMatches& history_matches,
       bool prevent_inline_autocomplete,
       int* max_match_score);
 
@@ -64,6 +66,12 @@ class HistoryQuickProvider : public HistoryProvider {
       const history::ScoredHistoryMatch& history_match,
       int* max_match_score);
 
+  // Determines the confidence of |match| by comparing the |raw_score| to the
+  // sum of the scores of |matches|. Returns a float in the range [0, 1].
+  static float CalculateConfidence(
+      const history::ScoredHistoryMatch& match,
+      const history::ScoredHistoryMatches& matches);
+
   // Returns the index that should be used for history lookups.
   history::InMemoryURLIndex* GetIndex();