Introduce Range::dispose() for prompt detachment from owner Document.

Source/core/dom/Range.h

Index: Source/core/dom/Range.h
diff --git a/Source/core/dom/Range.h b/Source/core/dom/Range.h
index 9cf22a6fafc1d998f06eb5081dea6bf6e8f43b8c..c5ba37e1a803153a7601da0f071f403bc55310de 100644
--- a/Source/core/dom/Range.h
+++ b/Source/core/dom/Range.h
@@ -64,6 +64,7 @@ public:
 #if !ENABLE(OILPAN) || !defined(NDEBUG)
     ~Range();
 #endif
+    void dispose();
 
     Document& ownerDocument() const { ASSERT(m_ownerDocument); return *m_ownerDocument.get(); }
     Node* startContainer() const { return m_start.container(); }