Omnibox: Add Field Trial to Skip HistoryURL Provider Searching its Database

components/omnibox/browser/history_url_provider.h

 // Copyright (c) 2012 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 COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_
 #define COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 315 matching lines @@
       int relevance);
 
   AutocompleteProviderListener* listener_;
 
   // Params for the current query.  The provider should not free this directly;
   // instead, it is passed as a parameter through the history backend, and the
   // parameter itself is freed once it's no longer needed.  The only reason we
   // keep this member is so we can set the cancel bit on it.
   HistoryURLProviderParams* params_;
 
+  // Whether to query the history URL database to match.  Even if false, we
+  // still use the URL database to decide if the URL-what-you-typed was visited
+  // before or not.  If false, the only possible result that HistoryURL provider
+  // can return is URL-what-you-typed.  This variable is not part of params_
+  // because it never changes after the HistoryURLProvider is initialized.
+  // It's used to aid the possible transition to get all URLs from history to
+  // be scored in the HistoryQuick provider only.
+  bool search_url_database_;
+
   // Params controlling experimental behavior of this provider.
   HUPScoringParams scoring_params_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(HistoryURLProvider);
 };
 
 #endif  // COMPONENTS_OMNIBOX_BROWSER_HISTORY_URL_PROVIDER_H_