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

ios/chrome/app/startup/ios_chrome_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.
 
 #include "ios/chrome/app/startup/ios_chrome_main.h"
 
 #import <UIKit/UIKit.h>
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/time/time.h"
 #include "ios/web/public/app/web_main_runner.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 base::Time* g_start_time;
 }  // namespace
 
 IOSChromeMain::IOSChromeMain() {
   web_main_runner_.reset(web::WebMainRunner::Create());
 
   web::WebMainParams main_params = web::WebMainParams(&main_delegate_);
 // Copy NSProcessInfo arguments into WebMainParams in debug only, since
 // command line should be meaningless outside of developer builds.
@@ skipping 31 matching lines @@
 void IOSChromeMain::InitStartTime() {
   DCHECK(!g_start_time);
   g_start_time = new base::Time(base::Time::Now());
 }
 
 // static
 const base::Time& IOSChromeMain::StartTime() {
   CHECK(g_start_time);
   return *g_start_time;
 }