[import] support document.stylesheets in imported documents.

Source/core/dom/StyleSheetCollection.h

Index: Source/core/dom/StyleSheetCollection.h
diff --git a/Source/core/dom/StyleSheetCollection.h b/Source/core/dom/StyleSheetCollection.h
index eddab7c451539ced7b86d4ea8deb640796cd6471..5a2b44e3a807dbe040e156fdcd2737be16dfc57c 100644
--- a/Source/core/dom/StyleSheetCollection.h
+++ b/Source/core/dom/StyleSheetCollection.h
@@ -30,6 +30,7 @@
 
 #include "core/dom/Document.h"
 #include "core/dom/DocumentOrderedList.h"
+#include "core/dom/DocumentStyleSheetCollector.h"
 #include "core/dom/StyleSheetScopingNodeList.h"
 #include "core/dom/TreeScope.h"
 #include "wtf/FastAllocBase.h"
@@ -65,10 +66,13 @@ public:
     const Vector<RefPtr<StyleSheet> >& styleSheetsForStyleSheetList() const { return m_styleSheetsForStyleSheetList; }
 
     void swap(StyleSheetCollectionBase&);
+    void swapSheetsForSheetList(Vector<RefPtr<StyleSheet> >&);
     void appendActiveStyleSheets(const Vector<RefPtr<CSSStyleSheet> >&);
     void appendActiveStyleSheet(CSSStyleSheet*);
     void appendSheetForList(StyleSheet*);
 
+    DocumentStyleSheetCollector collector();
+
 protected:
     Vector<RefPtr<StyleSheet> > m_styleSheetsForStyleSheetList;
     Vector<RefPtr<CSSStyleSheet> > m_activeAuthorStyleSheets;