Remove Enable Exits On Suspend flags on iOS

ios/chrome/app/UIApplication+ExitsOnSuspend.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.
-
-#if !defined(NDEBUG)
-
-#import "ios/chrome/app/UIApplication+ExitsOnSuspend.h"
-
-#include "base/ios/block_types.h"
-#include "base/logging.h"
-#include "base/threading/thread_restrictions.h"
-
-NSString* const kExitsOnSuspend = @"EnableExitsOnSuspend";
-
-namespace {
-int backgroundTasksCount = 0;
-UIBackgroundTaskIdentifier countTaskIdentifier = UIBackgroundTaskInvalid;
-
-// Perform a block on the main thread. Asynchronously if the thread is not the
-// main thread, synchronously if the thread is the main thread.
-void ExecuteBlockOnMainThread(ProceduralBlock block) {
-  if ([NSThread isMainThread])
-    block();
-  else
-    dispatch_async(dispatch_get_main_queue(), block);
-}
-}  // namespace
-
-// Category defining interposing methods. These methods keep a tally of the
-// background tasks count.
-@implementation UIApplication (BackgroundTasksCounter)
-
-// Method to replace -beginBackgroundTaskWithExpirationHandler:. The original
-// method is called within.
-- (UIBackgroundTaskIdentifier)
-    cr_interpose_beginBackgroundTaskWithExpirationHandler:
-        (ProceduralBlock)handler {
-  UIBackgroundTaskIdentifier identifier =
-      [self cr_interpose_beginBackgroundTaskWithExpirationHandler:handler];
-  if (identifier != UIBackgroundTaskInvalid) {
-    ExecuteBlockOnMainThread(^{
-      backgroundTasksCount++;
-    });
-  }
-  return identifier;
-}
-
-// Method to replace -endBackgroundTask:. The original method is called within.
-- (void)cr_interpose_endBackgroundTask:(UIBackgroundTaskIdentifier)identifier {
-  if (identifier != UIBackgroundTaskInvalid)
-    ExecuteBlockOnMainThread(^{
-      backgroundTasksCount--;
-    });
-  [self cr_interpose_endBackgroundTask:identifier];
-}
-
-@end
-
-@interface UIApplication (ExitsOnSuspend_Private)
-// Terminate the app immediately. exit(0) is used.
-- (void)cr_terminateImmediately;
-// Terminate the app via -cr_terminateImmediately when the background tasks
-// count is one. The remaining task is the count observation task.
-- (void)cr_terminateWhenCountIsOne;
-@end
-
-@implementation UIApplication (ExitsOnSuspend)
-
-- (void)cr_terminateWhenDoneWithBackgroundTasks {
-  // Add a background task for the count observation.
-  DCHECK(countTaskIdentifier == UIBackgroundTaskInvalid);
-  countTaskIdentifier = [self beginBackgroundTaskWithExpirationHandler:^{
-    // If we get to the end of the 10 minutes, exit.
-    [self cr_terminateImmediately];
-  }];
-
-  [self cr_terminateWhenCountIsOne];
-}
-
-- (void)cr_cancelTermination {
-  [NSObject
-      cancelPreviousPerformRequestsWithTarget:self
-                                     selector:@selector(
-                                                  cr_terminateWhenCountIsOne)
-                                       object:nil];
-
-  // Cancel the count observation background task.
-  [self endBackgroundTask:countTaskIdentifier];
-  countTaskIdentifier = UIBackgroundTaskInvalid;
-}
-
-#pragma mark - Private
-
-- (void)cr_terminateImmediately {
-  DVLOG(1) << "App exited when suspended after running background tasks.";
-  // exit(0) will trigger at_exit handlers. Some need to be run on a IOAllowed
-  // thread, such as file_util::MemoryMappedFile::CloseHandles().
-  base::ThreadRestrictions::SetIOAllowed(true);
-  exit(0);
-}
-
-- (void)cr_terminateWhenCountIsOne {
-  if (backgroundTasksCount <= 1)
-    [self cr_terminateImmediately];
-  [self performSelector:_cmd withObject:nil afterDelay:1];
-}
-
-@end
-
-#endif  // !defined(NDEBUG)