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

ios/chrome/browser/google/google_logo_service.mm

 // Copyright 2014 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 "ios/chrome/browser/google/google_logo_service.h"
 
 #import <Foundation/Foundation.h>
 
 #include "base/bind.h"
 #include "base/strings/sys_string_conversions.h"
@@ skipping 74 matching lines @@
     : browser_state_(browser_state) {}
 
 GoogleLogoService::~GoogleLogoService() {}
 
 void GoogleLogoService::GetLogo(search_provider_logos::LogoObserver* observer) {
   TemplateURLService* template_url_service =
       ios::TemplateURLServiceFactory::GetForBrowserState(browser_state_);
   if (!template_url_service)
     return;
 
-  TemplateURL* template_url = template_url_service->GetDefaultSearchProvider();
+  const TemplateURL* template_url =
+      template_url_service->GetDefaultSearchProvider();
   if (!template_url ||
       !template_url->url_ref().HasGoogleBaseURLs(
           template_url_service->search_terms_data()))
     return;
 
   if (!logo_tracker_) {
     logo_tracker_.reset(new LogoTracker(
         DoodleDirectory(),
         web::WebThread::GetTaskRunnerForThread(web::WebThread::FILE),
         web::WebThread::GetBlockingPool(), browser_state_->GetRequestContext(),
@@ skipping 21 matching lines @@
     cached_metadata_ = empty_metadata;
   }
 }
 
 search_provider_logos::Logo GoogleLogoService::GetCachedLogo() {
   search_provider_logos::Logo logo;
   logo.image = cached_image_;
   logo.metadata = cached_metadata_;
   return logo;
 }