Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderTextControlMultiLine.h

Index: Source/core/rendering/RenderTextControlMultiLine.h
diff --git a/Source/core/rendering/RenderTextControlMultiLine.h b/Source/core/rendering/RenderTextControlMultiLine.h
index 6ca01671bd445e2f1510264dccde478e6f6fa0d3..2486f542d5cdfee840008ff7ffd67e57041493ba 100644
--- a/Source/core/rendering/RenderTextControlMultiLine.h
+++ b/Source/core/rendering/RenderTextControlMultiLine.h
@@ -48,14 +48,7 @@ private:
     virtual RenderObject* layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope&);
 };
 
-inline RenderTextControlMultiLine* toRenderTextControlMultiLine(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isTextArea());
-    return static_cast<RenderTextControlMultiLine*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderTextControlMultiLine(const RenderTextControlMultiLine*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderTextControlMultiLine, isTextArea());
 
 }