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

ios/chrome/app/chrome_exe_main.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 <UIKit/UIKit.h>
 
 #include "base/at_exit.h"
 #include "base/debug/crash_logging.h"
 #include "components/crash/core/common/crash_keys.h"
 #include "ios/chrome/app/startup/ios_chrome_main.h"
 #include "ios/chrome/browser/crash_report/breakpad_helper.h"
 #include "ios/chrome/browser/crash_report/crash_keys.h"
 #include "ios/chrome/common/channel_info.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 NSString* const kUIApplicationDelegateInfoKey = @"UIApplicationDelegate";
 
 void StartCrashController() {
   @autoreleasepool {
     std::string channel_string = GetChannelString();
 
     RegisterChromeIOSCrashKeys();
     base::debug::SetCrashKeyValue(crash_keys::kChannel, channel_string);
@@ skipping 37 matching lines @@
   // The Crash Controller is started here even if the user opted out since we
   // don't have yet preferences. Later on it is stopped if the user opted out.
   // In any case reports are not sent if the user opted out.
   StartCrashController();
 
   // Always ignore SIGPIPE.  We check the return value of write().
   CHECK_NE(SIG_ERR, signal(SIGPIPE, SIG_IGN));
 
   return RunUIApplicationMain(argc, argv);
 }