ServiceWorker: add ServiceWorkerClients.claim() support (1/3).

public/platform/WebServiceWorkerClientsClaimCallbacks.h

Index: public/platform/WebServiceWorkerClientsClaimCallbacks.h
diff --git a/public/platform/WebServiceWorkerClientsClaimCallbacks.h b/public/platform/WebServiceWorkerClientsClaimCallbacks.h
new file mode 100644
index 0000000000000000000000000000000000000000..90b8b89ee90c58b5d75bed7a7a42253861e2281b
--- /dev/null
+++ b/public/platform/WebServiceWorkerClientsClaimCallbacks.h
@@ -0,0 +1,18 @@
+// 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 WebServiceWorkerClientsClaimCallbacks_h
+#define WebServiceWorkerClientsClaimCallbacks_h
+
+#include "public/platform/WebCallbacks.h"
+
+namespace blink {
+
+struct WebServiceWorkerError;
+
+using WebServiceWorkerClientsClaimCallbacks = WebCallbacks<void, WebServiceWorkerError>;
+
+} // namespace blink
+
+#endif // WebServiceWorkerClientsClaimCallbacks_h