Oilpan: dispose an HTMLImportsController on document detach/removal.

Source/core/html/imports/HTMLImportTreeRoot.h

 // 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 HTMLImportTreeRoot_h
 #define HTMLImportTreeRoot_h
 
 #include "core/html/imports/HTMLImport.h"
 #include "platform/Timer.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace blink {
 
 class HTMLImportChild;
 class KURL;
 
 class HTMLImportTreeRoot : public HTMLImport {
 public:
     static PassOwnPtrWillBeRawPtr<HTMLImportTreeRoot> create(Document*);
 
     virtual ~HTMLImportTreeRoot();
+    void dispose();
 
     // HTMLImport
     virtual Document* document() const override;
     virtual bool isDone() const override;
     virtual void stateWillChange() override;
     virtual void stateDidChange() override;
 
     void scheduleRecalcState();
 
     HTMLImportChild* add(PassOwnPtrWillBeRawPtr<HTMLImportChild>);
@@ skipping 12 matching lines @@
     // List of import which has been loaded or being loaded.
     typedef WillBeHeapVector<OwnPtrWillBeMember<HTMLImportChild>> ImportList;
     ImportList m_imports;
 };
 
 DEFINE_TYPE_CASTS(HTMLImportTreeRoot, HTMLImport, import, import->isRoot(), import.isRoot());
 
 }
 
 #endif