WIP bindings: Add support for the record<K,V> WebIDL type.

third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl

Index: third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl
diff --git a/third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl b/third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl
index 8a16e16dde0a9a36542222b9bc0ebf4c0dc5db22..54da53bb08b86573ee98324f546e74ab193c80e7 100644
--- a/third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl
+++ b/third_party/WebKit/Source/bindings/templates/callback_function.h.tmpl
@@ -38,6 +38,12 @@ class {{exported}}{{cpp_class}} final : public GarbageCollectedFinalized<{{cpp_c
   TraceWrapperV8Reference<v8::Function> m_callback;
 };
 
+template <>
+struct NativeValueTraits<{{cpp_class}}> {
+  using ImplType = {{cpp_class}};
+  {{exported}}static {{cpp_class}}* nativeValue(v8::Isolate*, v8::Local<v8::Value>, ExceptionState&);
+};
+
 }  // namespace blink
 
 #endif  // {{cpp_class}}_h