Move content/child/background_sync to Blink.

third_party/WebKit/public/platform/modules/background_sync/WebSyncClient.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 WebSyncClient_h
 #define WebSyncClient_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/modules/background_sync/WebSyncError.h"
-#include "public/platform/modules/background_sync/WebSyncProvider.h"
 
 namespace blink {
 
 class WebServiceWorkerRegistration;
 struct WebSyncRegistration;
 
 class WebSyncClient {
  public:
   virtual ~WebSyncClient() {}
 
   // Ownership of the WebServiceWorkerRegistration is not transferred.
   // Ownership of the callbacks is transferred to the client.
   virtual void registerSync(WebServiceWorkerRegistration*,
                             WebSyncRegistrationCallbacks*) = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebSyncClient_h