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

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

 // 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.
 
 #import "ios/chrome/browser/ui/ntp/google_landing_controller.h"
 
 #include <algorithm>
 
 #include "base/i18n/case_conversion.h"
 #import "base/ios/weak_nsobject.h"
@@ skipping 574 matching lines @@
 - (void)reparentToolbarController {
   [_headerView reparentToolbarController];
 }
 
 - (BOOL)isShowingLogo {
   return [_doodleController isShowingLogo];
 }
 
 - (void)updateLogoAndFakeboxDisplay {
   BOOL showLogo = NO;
-  TemplateURL* defaultURL = _templateURLService->GetDefaultSearchProvider();
+  const TemplateURL* defaultURL =
+      _templateURLService->GetDefaultSearchProvider();
   if (defaultURL) {
     showLogo =
         defaultURL->GetEngineType(_templateURLService->search_terms_data()) ==
         SEARCH_ENGINE_GOOGLE;
   }
 
   if (self.showingLogo != showLogo) {
     [_doodleController setShowingLogo:showLogo];
     if (_viewLoaded) {
       [self updateSubviewFrames];
@@ skipping 1100 matching lines @@
   if (!view) {
     return nil;
   }
   if ([view isKindOfClass:aClass]) {
     return view;
   }
   return [self nearestAncestorOfView:[view superview] withClass:aClass];
 }
 
 @end