Implement Permission change observing in Blink.

public/platform/modules/permissions/WebPermissionObserver.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 WebPermissionObserver_h
+#define WebPermissionObserver_h
+
+#include "public/platform/modules/permissions/WebPermissionStatus.h"
+#include "public/platform/modules/permissions/WebPermissionType.h"
+
+namespace blink {
+
+class WebPermissionObserver {
+public:
+    virtual void permissionChanged(WebPermissionType, WebPermissionStatus) = 0;
+};
+
+} // namespace blink
+
+#endif // WebPermissionObserver_h