Use tighter typing for Document::ownerElement() return value

Source/core/rendering/RenderView.cpp

Index: Source/core/rendering/RenderView.cpp
diff --git a/Source/core/rendering/RenderView.cpp b/Source/core/rendering/RenderView.cpp
index 4e82b3293843666b51d6239e608faa56946e2f1b..07d63894afa099a864db6291c6b6b9d20d573c79 100644
--- a/Source/core/rendering/RenderView.cpp
+++ b/Source/core/rendering/RenderView.cpp
@@ -453,7 +453,7 @@ void RenderView::invalidatePaintForRectangle(const LayoutRect& paintInvalidation
 
     // We always just invalidate the root view, since we could be an iframe that is clipped out
     // or even invisible.
-    Element* owner = document().ownerElement();
+    HTMLFrameOwnerElement* owner = document().ownerElement();
     if (layer()->compositingState() == PaintsIntoOwnBacking) {
         layer()->paintInvalidator().setBackingNeedsPaintInvalidationInRect(paintInvalidationRect);
     } else if (!owner) {