blink: Cleanup class/struct forward declarations

third_party/WebKit/public/platform/modules/push_messaging/WebPushClient.h

 // Copyright 2014 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 WebPushClient_h
 #define WebPushClient_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/modules/push_messaging/WebPushError.h"
 #include "public/platform/modules/push_messaging/WebPushProvider.h"
 #include <memory>
 
 namespace blink {
 
 class WebServiceWorkerRegistration;
-struct WebPushSubscription;
 struct WebPushSubscriptionOptions;
 
 class WebPushClient {
  public:
   virtual ~WebPushClient() {}
 
   // Ownership of the WebServiceWorkerRegistration is not transferred.
   // Ownership of the callbacks is transferred to the client.
   virtual void subscribe(WebServiceWorkerRegistration*,
                          const WebPushSubscriptionOptions&,
                          std::unique_ptr<WebPushSubscriptionCallbacks>) = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebPushClient_h