[ObjC ARC] Converts ios/chrome/browser/ui/main:unit_tests to ARC.

ios/chrome/browser/ui/main/browser_view_wrangler_unittest.mm

 // Copyright 2016 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/main/browser_view_wrangler.h"
 
 #import <UIKit/UIKit.h>
 
-#include "base/mac/scoped_nsobject.h"
 #include "ios/chrome/browser/browser_state/test_chrome_browser_state.h"
 #import "ios/chrome/browser/tabs/tab_model.h"
 #import "ios/chrome/browser/ui/browser_view_controller.h"
 #include "ios/web/public/test/test_web_thread_bundle.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 class BrowserViewWranglerTest : public PlatformTest {
  protected:
   BrowserViewWranglerTest() {
     TestChromeBrowserState::Builder test_cbs_builder;
     chrome_browser_state_ = test_cbs_builder.Build();
   }
 
   web::TestWebThreadBundle thread_bundle_;
   std::unique_ptr<TestChromeBrowserState> chrome_browser_state_;
 };
 
 TEST_F(BrowserViewWranglerTest, TestInitNilObserver) {
-  base::scoped_nsobject<BrowserViewWrangler> wrangler(
-      [[BrowserViewWrangler alloc]
-          initWithBrowserState:chrome_browser_state_.get()
-              tabModelObserver:nil]);
+  BrowserViewWrangler* wrangler = [[BrowserViewWrangler alloc]
+      initWithBrowserState:chrome_browser_state_.get()
+          tabModelObserver:nil];
 
   // Test that BVC and tab model are created on demand.
   BrowserViewController* bvc = [wrangler mainBVC];
   EXPECT_NE(bvc, nil);
 
   TabModel* tabModel = [wrangler mainTabModel];
   EXPECT_NE(tabModel, nil);
 
   // Test that once created the BVC and tab model aren't re-created.
   EXPECT_EQ(bvc, [wrangler mainBVC]);
   EXPECT_EQ(tabModel, [wrangler mainTabModel]);
 
   // Test that the OTR objects are (a) OTR and (b) not the same as the non-OTR
   // objects.
   EXPECT_NE(bvc, [wrangler otrBVC]);
   EXPECT_NE(tabModel, [wrangler otrTabModel]);
   EXPECT_TRUE([wrangler otrTabModel].browserState->IsOffTheRecord());
 }
 
 }  // namespace