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

ios/chrome/browser/ui/browser_view_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/browser_view_controller.h"
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 #import <PassKit/PassKit.h>
 #import <Photos/Photos.h>
@@ skipping 2613 matching lines @@
       Record(ACTION_OPEN_IMAGE_IN_NEW_TAB, isImage, isLink);
       [weakSelf webPageOrderedOpen:imageUrl
                           referrer:referrer
                       inBackground:true
                           appendTo:kCurrentTab];
     };
     [_contextMenuCoordinator addItemWithTitle:title action:action];
 
     TemplateURLService* service =
         ios::TemplateURLServiceFactory::GetForBrowserState(_browserState);
-    TemplateURL* defaultURL = service->GetDefaultSearchProvider();
+    const TemplateURL* defaultURL = service->GetDefaultSearchProvider();
     if (defaultURL && !defaultURL->image_url().empty() &&
         defaultURL->image_url_ref().IsValid(service->search_terms_data())) {
       title = l10n_util::GetNSStringF(IDS_IOS_CONTEXT_MENU_SEARCHWEBFORIMAGE,
                                       defaultURL->short_name());
       action = ^{
         Record(ACTION_SEARCH_BY_IMAGE, isImage, isLink);
         [weakSelf searchByImageAtURL:imageUrl referrer:referrer];
       };
       [_contextMenuCoordinator addItemWithTitle:title action:action];
     }
@@ skipping 544 matching lines @@
                          preserveAspectRatio:YES
                                    trimToFit:NO];
     imageData = UIImageJPEGRepresentation(image, 1.0);
   }
 
   char const* bytes = reinterpret_cast<const char*>([imageData bytes]);
   std::string byteString(bytes, [imageData length]);
 
   TemplateURLService* templateUrlService =
       ios::TemplateURLServiceFactory::GetForBrowserState(_browserState);
-  TemplateURL* defaultURL = templateUrlService->GetDefaultSearchProvider();
+  const TemplateURL* defaultURL =
+      templateUrlService->GetDefaultSearchProvider();
   DCHECK(!defaultURL->image_url().empty());
   DCHECK(defaultURL->image_url_ref().IsValid(
       templateUrlService->search_terms_data()));
   TemplateURLRef::SearchTermsArgs search_args(base::ASCIIToUTF16(""));
   search_args.image_url = imageURL;
   search_args.image_thumbnail_content = byteString;
 
   // Generate the URL and populate |post_content| with the content type and
   // HTTP body for the request.
   TemplateURLRef::PostContent post_content;
@@ skipping 1964 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end