Add IDL and initial Blink API for Background Sync

public/platform/modules/background_sync/WebSyncProvider.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 WebSyncProvider_h
 #define WebSyncProvider_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/WebCommon.h"
+#include "public/platform/WebString.h"
+#include "public/platform/WebVector.h"
 
 namespace blink {
 
 class WebServiceWorkerRegistration;
 struct WebSyncError;
 struct WebSyncRegistration;
-struct WebSyncRegistrationOptions;
 
 using WebSyncRegistrationCallbacks = WebCallbacks<WebSyncRegistration, WebSyncError>;
+using WebSyncUnregistrationCallbacks = WebCallbacks<bool, WebSyncError>;
+using WebSyncGetRegistrationsCallbacks = WebCallbacks<WebVector<WebSyncRegistration>, WebSyncError>;
 
 class WebSyncProvider {
 public:
     virtual ~WebSyncProvider() { }
 
     // Takes ownership of the WebSyncRegistrationCallbacks.
-    // Does not take ownership of the WebServiceWorkerRegistration.
-    virtual void registerBackgroundSync(const WebSyncRegistrationOptions*, WebSyncRegistrationCallbacks*) = 0;
+    virtual void registerBackgroundSync(const WebSyncRegistration*, WebSyncRegistrationCallbacks*) = 0;
+
+    // Takes ownership of the WebSyncUnregistrationCallbacks.
+    virtual void unregisterBackgroundSync(const WebString&, WebSyncUnregistrationCallbacks*) = 0;
+
+    // Takes ownership of the WebSyncRegistrationCallbacks.
+    virtual void getRegistration(const WebString&, WebSyncRegistrationCallbacks*) = 0;
+
+    // Takes ownership of the WebSyncGetRegistrationsCallbacks.
+    virtual void getRegistrations(WebSyncGetRegistrationsCallbacks*) = 0;
 };
 
 } // namespace blink
 
 #endif // WebSyncProvider_h