Show notifications even when the app is focused

It's a little icky to be taking over global state (NSUserNotificationCenter's
delegate) like this, but until we have evidence that it gets in someone's way
it's the pragmatic thing to do.

brightray/browser/notification_presenter_mac.h

@@ -3,7 +3,9 @@
 
 #import "browser/notification_presenter.h"
 
-#import "base/compiler_specific.h"
+#import "base/memory/scoped_nsobject.h"
+
+@class BRYUserNotificationCenterDelegate;
 
 namespace brightray {
 
@@ -16,6 +18,9 @@ class NotificationPresenterMac : public NotificationPresenter {
       const content::ShowDesktopNotificationHostMsgParams&,
       int render_process_id,
       int render_view_id) OVERRIDE;
+
+ private:
+  scoped_nsobject<BRYUserNotificationCenterDelegate> delegate_;
 };
 
 }

brightray/browser/notification_presenter_mac.mm

@@ -6,13 +6,18 @@
 
 #import <Foundation/Foundation.h>
 
+@interface BRYUserNotificationCenterDelegate : NSObject <NSUserNotificationCenterDelegate>
+@end
+
 namespace brightray {
 
 NotificationPresenter* NotificationPresenter::Create() {
   return new NotificationPresenterMac;
 }
 
-NotificationPresenterMac::NotificationPresenterMac() {
+NotificationPresenterMac::NotificationPresenterMac()
+    : delegate_([[BRYUserNotificationCenterDelegate alloc] init]) {
+  NSUserNotificationCenter.defaultUserNotificationCenter.delegate = delegate_;
 }
 
 NotificationPresenterMac::~NotificationPresenterMac() {
@@ -37,3 +42,12 @@ void NotificationPresenterMac::ShowNotification(
 }
 
 }
+
+@implementation BRYUserNotificationCenterDelegate
+
+- (BOOL)userNotificationCenter:(NSUserNotificationCenter *)center shouldPresentNotification:(NSUserNotification *)notification {
+  // Display notifications even if the app is active.
+  return YES;
+}
+
+@end