Have SearchProvider look up the omnibox start margin directly.

chrome/browser/autocomplete/search_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.
 //
 // This file contains the Search autocomplete provider.  This provider is
 // responsible for all autocomplete entries that start with "Search <engine>
 // for ...", including searching for the current input string, search
 // history, and search suggestions.  An instance of it gets created and
 // managed by the autocomplete controller.
 
@@ skipping 76 matching lines @@
       const AutocompleteInput& input,
       bool is_keyword,
       int accepted_suggestion,
       int omnibox_start_margin,
       bool append_extra_query_params);
 
   // AutocompleteProvider:
   virtual void AddProviderInfo(ProvidersInfo* provider_info) const OVERRIDE;
   virtual void ResetSession() OVERRIDE;
 
-  // Update the omnibox start margin used to generate search suggestion URLs.
-  void SetOmniboxStartMargin(int omnibox_start_margin);
-
   bool field_trial_triggered_in_session() const {
     return field_trial_triggered_in_session_;
   }
 
  private:
   // TODO(hfung): Remove ZeroSuggestProvider as a friend class after
   // refactoring common code to a new base class.
   friend class SearchProviderTest;
   friend class ZeroSuggestProvider;
   FRIEND_TEST_ALL_PREFIXES(SearchProviderTest, NavigationInline);
@@ skipping 410 matching lines @@
   // to true if either the default provider or keyword provider has completed
   // and their corresponding suggest response contained
   // '"google:fieldtrialtriggered":true'.
   // If the autocomplete query has not returned, this field is set to false.
   bool field_trial_triggered_;
 
   // Same as above except that it is maintained across the current Omnibox
   // session.
   bool field_trial_triggered_in_session_;
 
-  // Start margin of the omnibox. Used to construct search URLs.
-  int omnibox_start_margin_;
-
   // If true, search history query suggestions will score low enough that
   // they will not be inlined.
   bool prevent_search_history_inlining_;
 
   DISALLOW_COPY_AND_ASSIGN(SearchProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_SEARCH_PROVIDER_H_