Have SearchProvider look up the omnibox start margin directly.

chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.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 CHROME_BROWSER_UI_COCOA_LOCATION_BAR_LOCATION_BAR_VIEW_MAC_H_
 #define CHROME_BROWSER_UI_COCOA_LOCATION_BAR_LOCATION_BAR_VIEW_MAC_H_
 
 #include <string>
 
 #import <Cocoa/Cocoa.h>
@@ skipping 135 matching lines @@
       const GURL& alternate_nav_url) OVERRIDE;
   virtual void OnChanged() OVERRIDE;
   virtual void OnSelectionBoundsChanged() OVERRIDE;
   virtual void OnInputInProgress(bool in_progress) OVERRIDE;
   virtual void OnKillFocus() OVERRIDE;
   virtual void OnSetFocus() OVERRIDE;
   virtual gfx::Image GetFavicon() const OVERRIDE;
   virtual string16 GetTitle() const OVERRIDE;
   virtual InstantController* GetInstant() OVERRIDE;
   virtual content::WebContents* GetWebContents() const OVERRIDE;
-  virtual gfx::Rect GetOmniboxBounds() const OVERRIDE;
 
   NSImage* GetKeywordImage(const string16& keyword);
 
   AutocompleteTextField* GetAutocompleteTextField() { return field_; }
 
 
   // content::NotificationObserver:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
@@ skipping 92 matching lines @@
   // Used to schedule a task for the first run info bubble.
   base::WeakPtrFactory<LocationBarViewMac> weak_ptr_factory_;
 
   // Used to change the visibility of the star decoration.
   BooleanPrefMember edit_bookmarks_enabled_;
 
   DISALLOW_COPY_AND_ASSIGN(LocationBarViewMac);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_LOCATION_BAR_LOCATION_BAR_VIEW_MAC_H_