Have SearchProvider look up the omnibox start margin directly.

chrome/browser/ui/omnibox/omnibox_controller.cc

 // 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.
 
 #include "chrome/browser/ui/omnibox/omnibox_controller.h"
 
 #include "base/metrics/histogram.h"
 #include "chrome/browser/autocomplete/autocomplete_classifier.h"
 #include "chrome/browser/autocomplete/autocomplete_match.h"
 #include "chrome/browser/autocomplete/search_provider.h"
@@ skipping 25 matching lines @@
 OmniboxController::~OmniboxController() {
 }
 
 void OmniboxController::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 {
   ClearPopupKeywordMode();
   popup_->SetHoveredLine(OmniboxPopupModel::kNoMatch);
 
-  if (chrome::IsInstantExtendedAPIEnabled()) {
-    autocomplete_controller_->search_provider()->
-        SetOmniboxStartMargin(omnibox_start_margin);
-  }
-
   // We don't explicitly clear OmniboxPopupModel::manually_selected_match, as
   // Start ends up invoking OmniboxPopupModel::OnResultChanged which clears it.
   autocomplete_controller_->Start(AutocompleteInput(
       user_text, cursor_position, string16(), current_url,
       current_page_classification, prevent_inline_autocomplete,
       prefer_keyword, allow_exact_keyword_match,
       AutocompleteInput::ALL_MATCHES));
 }
 
 void OmniboxController::OnResultChanged(bool default_match_changed) {
@@ skipping 43 matching lines @@
     if (profile_->GetNetworkPredictor()) {
       profile_->GetNetworkPredictor()->AnticipateOmniboxUrl(
           match.destination_url,
           predictors::AutocompleteActionPredictor::IsPreconnectable(match));
     }
     // We could prefetch the alternate nav URL, if any, but because there
     // can be many of these as a user types an initial series of characters,
     // the OS DNS cache could suffer eviction problems for minimal gain.
   }
 }