Create a stub NSUserNotificationCenter and make tests use it.

chrome/browser/notifications/stub_notification_center_mac.mm

+// 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.
+
+#import "chrome/browser/notifications/stub_notification_center_mac.h"
+
+#include "base/logging.h"
+#include "base/mac/scoped_nsobject.h"
+#include "chrome/browser/ui/cocoa/notifications/notification_constants_mac.h"
+
+@implementation StubNotificationCenter {
+  base::scoped_nsobject<NSMutableArray> alerts_;
+}
+
+- (instancetype)init {
+  if ((self = [super init])) {
+    alerts_.reset([[NSMutableArray alloc] init]);
+  }
+  return self;
+}
+
+// The default implementation adds some extra checks on what constructors can
+// be used. isKindOfClass bypasses all of that.
+- (BOOL)isKindOfClass:(Class)cls {
+  if ([cls isEqual:NSClassFromString(@"_NSConcreteUserNotificationCenter")]) {
+    return YES;
+  }
+  return [super isKindOfClass:cls];
+}
+
+- (void)deliverNotification:(NSUserNotification*)notification {
+  [alerts_ addObject:notification];
+}
+
+- (NSArray*)deliveredNotifications {
+  return [[alerts_ copy] autorelease];
+}
+
+- (void)removeDeliveredNotification:(NSUserNotification*)notification {
+  NSString* notificationId = [notification.userInfo
+      objectForKey:notification_constants::kNotificationId];
+  NSString* profileId = [notification.userInfo
+      objectForKey:notification_constants::kNotificationProfileId];
+  DCHECK(profileId);
+  DCHECK(notificationId);
+  for (NSUserNotification* toast in alerts_.get()) {
+    NSString* toastId =
+        [toast.userInfo objectForKey:notification_constants::kNotificationId];
+    NSString* persistentProfileId = [toast.userInfo
+        objectForKey:notification_constants::kNotificationProfileId];
+    if ([toastId isEqualToString:notificationId] &&
+        [persistentProfileId isEqualToString:profileId]) {
+      [alerts_ removeObject:toast];
+      break;
+    }
+  }
+}
+
+- (void)removeAllDeliveredNotifications {
+  [alerts_ removeAllObjects];
+}
+
+// Need to provide a nop implementation of setDelegate as it is
+// used during the setup of the bridge.
+- (void)setDelegate:(id<NSUserNotificationCenterDelegate>)delegate {
+}
+
+@end