Make RenderObject::style() return a const object

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 f4dca90fc4876a5238d641491ad1418ed2e8c3a1..0c3b3c38f5c037c655d34c95d28e04a520a11601 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -789,7 +789,7 @@ public:
     // that as the style for the root element, rather than obtaining it on our own. The reason for
     // this is that style may not have been associated with the elements yet - in which case it may
     // have been calculated on the fly (without associating it with the actual element) somewhere.
-    Element* viewportDefiningElement(RenderStyle* rootStyle = nullptr) const;
+    Element* viewportDefiningElement(const RenderStyle* rootStyle = nullptr) const;
 
     DocumentMarkerController& markers() const { return *m_markers; }