[Mac] Wrap NSUserActivity begin/end so that it can be called from common files

content/common/mac/app_nap_activity.mm

+// Copyright 2017 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 "content/common/mac/app_nap_activity.h"
+
+#import <Foundation/Foundation.h>
+
+#include "base/mac/scoped_nsobject.h"
+
+namespace content {
+
+namespace {
+
+NSString* const kActivityReason = @"Process foregrounded";
+const NSActivityOptions kActivityOptions =
+    (NSActivityUserInitiatedAllowingIdleSystemSleep |
+     NSActivityLatencyCritical) &
+    ~(NSActivitySuddenTerminationDisabled |
+      NSActivityAutomaticTerminationDisabled);
+
+}  // namespace
+
+struct AssertionWrapper {
+  base::scoped_nsobject<id> obj;
+};
+
+AppNapActivity::AppNapActivity() {
+  assertion_.reset(new AssertionWrapper());
+};
+
+AppNapActivity::~AppNapActivity() {
+  DCHECK(!assertion_->obj.get());
+};
+
+void AppNapActivity::Begin() {
+  DCHECK(!assertion_->obj.get());
+  id assertion =
+      [[NSProcessInfo processInfo] beginActivityWithOptions:kActivityOptions
+                                                     reason:kActivityReason];
+  assertion_->obj.reset([assertion retain]);
+}
+
+void AppNapActivity::End() {
+  id assertion = assertion_->obj.autorelease();
+  DCHECK(assertion);
+  [[NSProcessInfo processInfo] endActivity:assertion];
+}
+
+}  // namespace content