Remove non-const version of GetDefaultSearchProvider() and make all callers call the const version

ios/chrome/browser/ui/ntp/new_tab_page_controller.mm

 // Copyright 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.
 
 #import "ios/chrome/browser/ui/ntp/new_tab_page_controller.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #import "base/ios/weak_nsobject.h"
 #include "base/logging.h"
@@ skipping 335 matching lines @@
 }
 
 - (BOOL)wantsLocationBarHintText {
   // Always show hint text on iPhone.
   if (!IsIPadIdiom())
     return YES;
   // Always show the location bar hint text if the search engine is not Google.
   TemplateURLService* service =
       ios::TemplateURLServiceFactory::GetForBrowserState(browserState_);
   if (service) {
-    TemplateURL* defaultURL = service->GetDefaultSearchProvider();
+    const TemplateURL* defaultURL = service->GetDefaultSearchProvider();
     if (defaultURL &&
         defaultURL->GetEngineType(service->search_terms_data()) !=
             SEARCH_ENGINE_GOOGLE) {
       return YES;
     }
   }
 
   // Always return true when incognito.
   if (browserState_->IsOffTheRecord())
     return YES;
@@ skipping 364 matching lines @@
 
 - (void)updateNtpBarShadowForPanelController:
     (id<NewTabPagePanelProtocol>)ntpPanelController {
   if (currentController_ != ntpPanelController)
     return;
   [self.ntpView.tabBar
       setShadowAlpha:[ntpPanelController alphaForBottomShadow]];
 }
 
 @end