[import] support document.stylesheets in imported documents.

Source/core/dom/StyleEngine.cpp

Index: Source/core/dom/StyleEngine.cpp
diff --git a/Source/core/dom/StyleEngine.cpp b/Source/core/dom/StyleEngine.cpp
index 00005d3dd5f769912967767194a2197a9715be18..3b0256002d3724fd8a5b695becd68b4cb4c8fbc0 100644
--- a/Source/core/dom/StyleEngine.cpp
+++ b/Source/core/dom/StyleEngine.cpp
@@ -34,6 +34,7 @@
 #include "core/css/CSSStyleSheet.h"
 #include "core/css/StyleInvalidationAnalysis.h"
 #include "core/css/StyleSheetContents.h"
+#include "core/dom/DocumentStyleSheetCollector.h"
 #include "core/dom/Element.h"
 #include "core/dom/ProcessingInstruction.h"
 #include "core/dom/ShadowTreeStyleSheetCollection.h"
@@ -348,9 +349,13 @@ void StyleEngine::clearMediaQueryRuleSetStyleSheets()
     clearMediaQueryRuleSetOnTreeScopeStyleSheets(m_dirtyTreeScopes);
 }
 
-void StyleEngine::collectDocumentStyleSheets(DocumentStyleSheetCollector& collector)
+void StyleEngine::updateStyleSheetsInImport(DocumentStyleSheetCollector& parentCollector)
 {
-    m_documentStyleSheetCollection.collectStyleSheets(this, collector);
+    ASSERT(!isMaster());
+    Vector<RefPtr<StyleSheet> > sheetsForList;
+    DocumentStyleSheetCollector subcollector = parentCollector.subcollectorWith(sheetsForList);
+    m_documentStyleSheetCollection.collectStyleSheets(this, subcollector);
+    m_documentStyleSheetCollection.swapSheetsForSheetList(sheetsForList);
 }
 
 bool StyleEngine::updateActiveStyleSheets(StyleResolverUpdateMode updateMode)