Reduce the false positive rate for SafeBrowsing gethash requests

chrome/browser/safe_browsing/safe_browsing_database_bloom.h

 // Copyright (c) 2006-2008 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_SAFE_BROWSING_SAFE_BROWSING_DATABASE_BLOOM_H_
 #define CHROME_BROWSER_SAFE_BROWSING_SAFE_BROWSING_DATABASE_BLOOM_H_
 
 #include <deque>
 #include <list>
 #include <queue>
@@ skipping 63 matching lines @@
 
   // Called when the user's machine has resumed from a lower power state.
   virtual void HandleResume();
 
   // Returns true if we have successfully started the update transaction.
   virtual bool UpdateStarted();
   virtual void UpdateFinished(bool update_succeeded);
 
   virtual bool NeedToCheckUrl(const GURL& url);
 
+  // How many bits to use per item.  See the design doc for more information.
+  static const int kBloomFilterSizeRatio = 25;
+
  private:
   // Opens the database.
   bool Open();
 
   // Closes the database.
   bool Close();
 
   // Creates the SQL tables.
   bool CreateTables();
 
@@ skipping 157 matching lines @@
   // Lock for protecting access to the bloom filter and hash cache.
   Lock lookup_lock_;
 
   // A store for GetHash results that have not yet been written to the database.
   HashList pending_full_hashes_;
 
   DISALLOW_COPY_AND_ASSIGN(SafeBrowsingDatabaseBloom);
 };
 
 #endif  // CHROME_BROWSER_SAFE_BROWSING_SAFE_BROWSING_DATABASE_BLOOM_H_