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

content/common/mac/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/activity.h"
+
+#import <Foundation/Foundation.h>
+
+#include "base/mac/scoped_nsobject.h"
+
+static NSString* const kActivityReason = @"Process foregrounded";

[Robert Sesek, 2017/05/31 18:11:27]

optional: drop the static and move into the anonymous namespace, inside
|namespace content|

[lgrey, 2017/05/31 21:28:12]

Done.

+static const NSActivityOptions kActivityOptions =
+    (NSActivityUserInitiatedAllowingIdleSystemSleep |
+     NSActivityLatencyCritical) &
+    ~(NSActivitySuddenTerminationDisabled |
+      NSActivityAutomaticTerminationDisabled);
+
+namespace mac {
+
+class AssertionWrapper {

[Robert Sesek, 2017/05/31 18:11:26]

I think this could be a simple struct and just expose the member publicly, since
it's basically a private implementation detail.

[lgrey, 2017/05/31 21:28:12]

Done. Renamed the member |obj_| to avoid awkward
"assertion_->assertion_->whatever" though IMO it still looks really awkward. Any
suggestions for how to clean it up or do you think it's OK like this?

[Robert Sesek, 2017/05/31 22:21:56]

Nope, I think that's fine. |obj| or |ptr| would be appropriate.

+ public:
+  id get() { return assertion_.get(); };
+  id autorelease() { return assertion_.autorelease(); }
+  void reset(id obj) { assertion_.reset(obj); };
+
+ private:
+  base::scoped_nsobject<id> assertion_;
+};

[Robert Sesek, 2017/05/31 18:11:26]

nit: blank line after

[lgrey, 2017/05/31 21:28:12]

Done.

+Activity::Activity() {
+  assertion_.reset(new AssertionWrapper());
+};
+
+Activity::~Activity(){};

[Robert Sesek, 2017/05/31 18:11:26]

DCHECK(!assertion_.get()) ?

[lgrey, 2017/05/31 21:28:12]

Done.

+
+void Activity::Begin() {
+  DCHECK(!assertion_->get());
+  id assertion =
+      [[NSProcessInfo processInfo] beginActivityWithOptions:kActivityOptions
+                                                     reason:kActivityReason];
+  assertion_->reset([assertion retain]);
+}
+
+void Activity::End() {
+  id assertion = assertion_->autorelease();
+  DCHECK(assertion);
+  [[NSProcessInfo processInfo] endActivity:assertion];
+}
+}  // namespace mac