Have SearchProvider look up the omnibox start margin directly.

chrome/browser/ui/omnibox/omnibox_controller.h

 // Copyright 2013 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_UI_OMNIBOX_OMNIBOX_CONTROLLER_H_
 #define CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_CONTROLLER_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 30 matching lines @@
   virtual ~OmniboxController();
 
   // |current_url| is only set for mobile ports.
   void StartAutocomplete(
       string16 user_text,
       size_t cursor_position,
       const GURL& current_url,
       AutocompleteInput::PageClassification current_page_classification,
       bool prevent_inline_autocomplete,
       bool prefer_keyword,
-      bool allow_exact_keyword_match,
-      int omnibox_start_margin) const;
+      bool allow_exact_keyword_match) const;
 
   // AutocompleteControllerDelegate:
   virtual void OnResultChanged(bool default_match_changed) OVERRIDE;
 
   AutocompleteController* autocomplete_controller() {
     return autocomplete_controller_.get();
   }
 
   // Set |current_match_| to an invalid value, indicating that we do not yet
   // have a valid match for the current text in the omnibox.
@@ skipping 33 matching lines @@
   // TODO(beaudoin): This AutocompleteMatch is used to let the OmniboxEditModel
   // know what it should display. Not every field is required for that purpose,
   // but the ones specifically needed are unclear. We should therefore spend
   // some time to extract these fields and use a tighter structure here.
   AutocompleteMatch current_match_;
 
   DISALLOW_COPY_AND_ASSIGN(OmniboxController);
 };
 
 #endif  // CHROME_BROWSER_UI_OMNIBOX_OMNIBOX_CONTROLLER_H_