Have Document::markers() return a reference

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index c895725783d710aa74c21a8c291e882ea0cd6c36..7677ad5384ee8f7eb47f2bcff9fce8cdf13758ce 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -783,7 +783,7 @@ public:
     // have been calculated on the fly (without associating it with the actual element) somewhere.
     Element* viewportDefiningElement(RenderStyle* rootStyle = 0) const;
 
-    DocumentMarkerController* markers() const { return m_markers.get(); }
+    DocumentMarkerController& markers() const { return *m_markers; }
 
     bool directionSetOnDocumentElement() const { return m_directionSetOnDocumentElement; }
     bool writingModeSetOnDocumentElement() const { return m_writingModeSetOnDocumentElement; }