Address a race condition in displaying notifications

content/browser/notifications/platform_notification_context_impl.h

 // Copyright 2015 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 CONTENT_BROWSER_NOTIFICATIONS_PLATFORM_NOTIFICATION_CONTEXT_IMPL_H_
 #define CONTENT_BROWSER_NOTIFICATIONS_PLATFORM_NOTIFICATION_CONTEXT_IMPL_H_
 
 #include <stdint.h>
 #include <memory>
 #include <set>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/time/time.h"
 #include "content/browser/notifications/notification_id_generator.h"
 #include "content/browser/service_worker/service_worker_context_observer.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/platform_notification_context.h"
 #include "third_party/WebKit/public/platform/modules/notifications/notification_service.mojom.h"
 
 class GURL;
 
 namespace base {
+class Clock;
 class SequencedTaskRunner;
 }
 
 namespace service_manager {
 struct BindSourceInfo;
 }
 
 namespace content {
 
 class BlinkNotificationServiceImpl;
@@ skipping 161 matching lines @@
   base::FilePath path_;
   BrowserContext* browser_context_;
 
   scoped_refptr<ServiceWorkerContextWrapper> service_worker_context_;
 
   scoped_refptr<base::SequencedTaskRunner> task_runner_;
   std::unique_ptr<NotificationDatabase> database_;
 
   NotificationIdGenerator notification_id_generator_;
 
+  std::unique_ptr<base::Clock> clock_;
+
+  // Stores the recently displayed notification ids together with the time at
+  // which they were displayed.
+  std::map<std::string, base::Time> recent_notifications_;
+
   // Indicates whether the database should be pruned when it's opened.
   bool prune_database_on_open_ = false;
 
   // The notification services are owned by the platform context, and will be
   // removed when either this class is destroyed or the Mojo pipe disconnects.
   std::vector<std::unique_ptr<BlinkNotificationServiceImpl>> services_;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformNotificationContextImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_NOTIFICATIONS_PLATFORM_NOTIFICATION_CONTEXT_IMPL_H_