Create a stub NSUserNotificationCenter and make tests use it.

chrome/browser/notifications/stub_notification_center_mac.h

Index: chrome/browser/notifications/stub_notification_center_mac.h
diff --git a/chrome/browser/notifications/stub_notification_center_mac.h b/chrome/browser/notifications/stub_notification_center_mac.h
new file mode 100644
index 0000000000000000000000000000000000000000..f817d5d8cabb0bb223226ae5293df4b06c565978
--- /dev/null
+++ b/chrome/browser/notifications/stub_notification_center_mac.h
@@ -0,0 +1,25 @@
+// Copyright 2016 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.
+
+#ifndef CHROME_BROWSER_NOTIFICATIONS_STUB_NOTIFICATION_CENTER_MAC_H_
+#define CHROME_BROWSER_NOTIFICATIONS_STUB_NOTIFICATION_CENTER_MAC_H_
+
+#import <AppKit/AppKit.h>
+
+@class NSUserNotificationCenterDelegate;

[Robert Sesek, 2016/11/01 17:09:01]

Not needed with AppKit.h?

[Miguel Garcia, 2016/11/07 14:18:41]

Peter asked the same thing. I swear it does not compile if I remove this :)

[Robert Sesek, 2016/11/07 16:16:50]

Oh, try Cocoa/Cocoa.h instead. NSUserNotificationCenter and friends are in
Foundation rather than AppKit. Cocoa is the forwarding header for both.

[Miguel Garcia, 2016/11/07 18:22:25]

Done, (NSUserNotificationCenterDelegate is a protocol so it has to be passed as
id<NSUserNotificationCenterDelegate> )

+
+// Stubs NSUserNotificationCenter so it can be used in tests without actually
+// displaying
+// notifications.

[Robert Sesek, 2016/11/01 17:09:01]

Join with previous line.

[Miguel Garcia, 2016/11/07 14:18:41]

Done.

+// Unlike the real class this is not a singleton and the lifecycle needs to be
+// handled
+// by the caller.

[Robert Sesek, 2016/11/01 17:09:01]

Join with previous line.

[Miguel Garcia, 2016/11/07 14:18:41]

Done.

+// See notification_platform_bridge_mac_unittest.mm for an example.
+@interface StubNotificationCenter : NSUserNotificationCenter
+- (instancetype)init;
+- (void)setDelegate:(NSUserNotificationCenterDelegate*)delegate;
+
+@end
+
+#endif  // CHROME_BROWSER_NOTIFICATIONS_STUB_NOTIFICATION_CENTER_MAC_H_