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

third_party/WebKit/public/web/WebOptionElement.h

Index: third_party/WebKit/public/web/WebOptionElement.h
diff --git a/third_party/WebKit/public/web/WebOptionElement.h b/third_party/WebKit/public/web/WebOptionElement.h
index dfbba7e730383727c2bcd206dab6911d2ef50b2f..bc98f982157dfb3336877823ca35f4133a6a5d11 100644
--- a/third_party/WebKit/public/web/WebOptionElement.h
+++ b/third_party/WebKit/public/web/WebOptionElement.h
@@ -39,7 +39,7 @@ namespace blink {
 class HTMLOptionElement;
 
 // Provides readonly access to some properties of a DOM option element node.
-class WebOptionElement : public WebElement {
+class WebOptionElement final : public WebElement {
 public:
     WebOptionElement() : WebElement() { }
     WebOptionElement(const WebOptionElement& element) : WebElement(element) { }
@@ -66,6 +66,8 @@ public:
 #endif
 };
 
+DECLARE_WEB_NODE_TYPE_CASTS(WebOptionElement);
+
 } // namespace blink
 
 #endif