Track confidence calculations better. Reduce minimum user text length.

chrome/browser/autocomplete/network_action_predictor.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_AUTOCOMPLETE_NETWORK_ACTION_PREDICTOR_H_
 #define CHROME_BROWSER_AUTOCOMPLETE_NETWORK_ACTION_PREDICTOR_H_
 #pragma once
 
 #include <map>
 
@@ skipping 123 matching lines @@
   // if the history service is available, or registers for the notification of
   // it becoming available.
   void CreateCaches(
       std::vector<NetworkActionPredictorDatabase::Row>* row_buffer);
 
   // Attempts to call DeleteOldEntries if the in-memory database has been loaded
   // by |service|. Returns success as a boolean.
   bool TryDeleteOldEntries(HistoryService* service);
 
   // Uses local caches to calculate an exact percentage prediction that the user
-  // will take a particular match given what they have typed.
-  double ExactAlgorithm(const string16& user_text,
-                        const AutocompleteMatch& match) const;
+  // will take a particular match given what they have typed. |is_in_db| is set
+  // to differentiate trivial zero results resulting from a match not being
+  // found from actual zero results where the calculation returns 0.0.
+  double CalculateConfidence(const string16& user_text,
+                             const AutocompleteMatch& match,
+                             bool* is_in_db) const;
 
   // Adds a row to the database and caches.
   void AddRow(const DBCacheKey& key,
               const NetworkActionPredictorDatabase::Row& row);
 
   // Updates a row in the database and the caches.
   void UpdateRow(DBCacheMap::iterator it,
                  const NetworkActionPredictorDatabase::Row& row);
 
   // Removes all rows from the database and caches.
@@ skipping 15 matching lines @@
 
   DBCacheMap db_cache_;
   DBIdCacheMap db_id_cache_;
 
   bool initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkActionPredictor);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_NETWORK_ACTION_PREDICTOR_H_