[ObjC ARC] Converts ios/chrome/app:unit_tests to ARC.

ios/chrome/app/main_application_delegate_unittest.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.
 
 #include "ios/chrome/app/main_application_delegate.h"
 
 #import <Foundation/Foundation.h>
 
 #import "base/mac/foundation_util.h"
-#include "base/mac/scoped_nsobject.h"
 #import "ios/chrome/app/chrome_overlay_window_testing.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "testing/platform_test.h"
 #import "third_party/ocmock/OCMock/OCMock.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 // Tests that the application does not crash if |applicationDidEnterBackground|
 // is called when the application is launched in background.
 // http://crbug.com/437307
 TEST(MainApplicationDelegateTest, CrashIfNotInitialized) {
   // Save both ChromeBrowserProvider as MainController register new instance.
   ios::ChromeBrowserProvider* stashed_chrome_browser_provider =
       ios::GetChromeBrowserProvider();
 
   id application = [OCMockObject niceMockForClass:[UIApplication class]];
   UIApplicationState backgroundState = UIApplicationStateBackground;
   [[[application stub] andReturnValue:OCMOCK_VALUE(backgroundState)]
       applicationState];
 
-  MainApplicationDelegate* delegate =
-      [[[MainApplicationDelegate alloc] init] autorelease];
+  MainApplicationDelegate* delegate = [[MainApplicationDelegate alloc] init];
   [delegate application:application didFinishLaunchingWithOptions:nil];
   [delegate applicationDidEnterBackground:application];
 
   // Clean up the size class recorder, which is created by the main window via
   // a previous call to |application:didFinishLaunchingWithOptions:|, to prevent
   // it from interfering with subsequent tests.
   ChromeOverlayWindow* mainWindow =
       base::mac::ObjCCastStrict<ChromeOverlayWindow>([delegate window]);
   [mainWindow unsetSizeClassRecorder];
 
   // Restore both ChromeBrowserProvider to its original value and destroy
   // instances created by MainController.
   DCHECK_NE(ios::GetChromeBrowserProvider(), stashed_chrome_browser_provider);
   delete ios::GetChromeBrowserProvider();
   ios::SetChromeBrowserProvider(stashed_chrome_browser_provider);
 }