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

third_party/WebKit/public/web/WebInputElement.h

Index: third_party/WebKit/public/web/WebInputElement.h
diff --git a/third_party/WebKit/public/web/WebInputElement.h b/third_party/WebKit/public/web/WebInputElement.h
index de38d60656bab882a4bd90346f1494c451f794c9..f374d40732b9f2f4c3bb11a30dd45e01b2bf812e 100644
--- a/third_party/WebKit/public/web/WebInputElement.h
+++ b/third_party/WebKit/public/web/WebInputElement.h
@@ -39,7 +39,7 @@ class HTMLInputElement;
 class WebElementCollection;
 
 // Provides readonly access to some properties of a DOM input element node.
-class WebInputElement : public WebFormControlElement {
+class WebInputElement final : public WebFormControlElement {
 public:
     WebInputElement() : WebFormControlElement() { }
     WebInputElement(const WebInputElement& element) : WebFormControlElement(element) { }
@@ -91,6 +91,8 @@ public:
 #endif
 };
 
+DECLARE_WEB_NODE_TYPE_CASTS(WebInputElement);
+
 // This returns 0 if the specified WebElement is not a WebInputElement.
 BLINK_EXPORT WebInputElement* toWebInputElement(WebElement*);
 // This returns 0 if the specified WebElement is not a WebInputElement.