Oilpan: dispose an HTMLImportsController on document detach/removal.

Source/core/html/imports/HTMLImportsController.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 61 matching lines @@
     size_t loaderCount() const { return m_loaders.size(); }
     HTMLImportLoader* loaderAt(size_t i) const { return m_loaders[i].get(); }
     Document* loaderDocumentAt(size_t) const;
     HTMLImportLoader* loaderFor(const Document&) const;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     HTMLImportChild* createChild(const KURL&, HTMLImportLoader*, HTMLImport* parent, HTMLImportChildClient*);
 
+    void dispose();
+
     OwnPtrWillBeMember<HTMLImportTreeRoot> m_root;
     typedef WillBeHeapVector<OwnPtrWillBeMember<HTMLImportLoader>> LoaderList;
     LoaderList m_loaders;
 };
 
 } // namespace blink
 
 #endif // HTMLImportsController_h