Make WebNode::to<Type>() (and toConst) casts contain type asserts.

third_party/WebKit/public/web/WebSelectElement.h

Index: third_party/WebKit/public/web/WebSelectElement.h
diff --git a/third_party/WebKit/public/web/WebSelectElement.h b/third_party/WebKit/public/web/WebSelectElement.h
index c60c80208456e76347cf94f18c128ef8b3b6a3c9..5afd57dcf5ac0fb7504af07bb4f8d7db15e196ea 100644
--- a/third_party/WebKit/public/web/WebSelectElement.h
+++ b/third_party/WebKit/public/web/WebSelectElement.h
@@ -40,7 +40,7 @@ namespace blink {
 class HTMLSelectElement;
 
 // Provides readonly access to some properties of a DOM select element node.
-class WebSelectElement : public WebFormControlElement {
+class WebSelectElement final : public WebFormControlElement {
 public:
     WebSelectElement() : WebFormControlElement() { }
     WebSelectElement(const WebSelectElement& element) : WebFormControlElement(element) { }
@@ -61,6 +61,8 @@ public:
 #endif
 };
 
+DECLARE_WEB_NODE_TYPE_CASTS(WebSelectElement);
+
 } // namespace blink
 
 #endif