Add APIs to protect critical tasks on iOS.

base/ios/scoped_critical_action.mm

Index: base/ios/scoped_critical_action.mm
diff --git a/base/ios/scoped_critical_action.mm b/base/ios/scoped_critical_action.mm
new file mode 100644
index 0000000000000000000000000000000000000000..734c0a215b6aa27c69d998c5882dfeb23a5536d2
--- /dev/null
+++ b/base/ios/scoped_critical_action.mm
@@ -0,0 +1,54 @@
+// Copyright (c) 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 "base/ios/scoped_critical_action.h"
+
+#import <UIKit/UIKit.h>
+
+#include "base/logging.h"
+#include "base/synchronization/lock.h"
+
+namespace base {
+namespace ios {
+
+// This implementation calls |beginBackgroundTaskWithExpirationHandler:| when
+// instantiated and |endBackgroundTask:| when destroyed, creating a scope whose
+// execution will continue (temporarily) even after the app is backgrounded.
+ScopedCriticalAction::ScopedCriticalAction() {
+  background_task_id_ = [[UIApplication sharedApplication]
+      beginBackgroundTaskWithExpirationHandler:^{
+        DLOG(WARNING) << "Background task with id " << background_task_id_
+                      << " expired.";
+        // Note if |endBackgroundTask:| is not called for each task before time
+        // expires, the system kills the application.
+        EndBackgroundTask();
+      }];
+  if (background_task_id_ == UIBackgroundTaskInvalid) {
+    DLOG(WARNING) <<
+        "beginBackgroundTaskWithExpirationHandler: returned an invalid ID";
+  } else {
+    VLOG(3) << "Beginning background task with id " << background_task_id_;
+  }
+}
+
+ScopedCriticalAction::~ScopedCriticalAction() {
+  EndBackgroundTask();
+}
+
+void ScopedCriticalAction::EndBackgroundTask() {
+  UIBackgroundTaskIdentifier task_id;
+  {
+    AutoLock lock_scope(background_task_id_lock_);
+    if (background_task_id_ == UIBackgroundTaskInvalid)
+      return;
+    task_id = background_task_id_;
+    background_task_id_ = UIBackgroundTaskInvalid;
+  }
+
+  VLOG(3) << "Ending background task with id " << task_id;
+  [[UIApplication sharedApplication] endBackgroundTask:task_id];
+}
+
+}  // namespace ios
+}  // namespace base