[POC-WIP] Link window focus tokens with ExecutionContext.

public/platform/WebServiceWorkerClientFocusCallback.h

Index: public/platform/WebServiceWorkerClientFocusCallback.h
diff --git a/public/platform/WebServiceWorkerClientFocusCallback.h b/public/platform/WebServiceWorkerClientFocusCallback.h
new file mode 100644
index 0000000000000000000000000000000000000000..3299b409b3d01e4f54fde2bac54244c2d22071bf
--- /dev/null
+++ b/public/platform/WebServiceWorkerClientFocusCallback.h
@@ -0,0 +1,18 @@
+// 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 WebServiceWorkerClientFocusCallback_h
+#define WebServiceWorkerClientFocusCallback_h
+
+#include "WebCallbacks.h"
+
+namespace blink {
+
+struct WebServiceWorkerError;
+
+typedef WebCallbacks<bool, WebServiceWorkerError> WebServiceWorkerClientFocusCallback;
+
+} // namespace blink
+
+#endif // WebServiceWorkerClientFocusCallback_h