Introduce toHTMLInputElement(Node*), and use it.

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index 91c3ec77cada10a9ad5c872fb67b8ec5ebfe345c..63183d3c5ad9690e188a468df1fb5bbe09c40ea5 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -1666,7 +1666,7 @@ void StyleResolver::adjustRenderStyle(RenderStyle* style, RenderStyle* parentSty
     if (e && e->isFormControlElement() && style->fontSize() >= 11) {
         // Don't apply intrinsic margins to image buttons. The designer knows how big the images are,
         // so we have to treat all image buttons as though they were explicitly sized.
-        if (!e->hasTagName(inputTag) || !static_cast<HTMLInputElement*>(e)->isImageButton())
+        if (!e->hasTagName(inputTag) || !toHTMLInputElement(e)->isImageButton())
             addIntrinsicMargins(style);
     }