IDL: Drop value conversion (V8 -> C++) macros from generated code

Source/bindings/templates/union.h

Index: Source/bindings/templates/union.h
diff --git a/Source/bindings/templates/union.h b/Source/bindings/templates/union.h
index 24d0bb7373bf82186c797fd43e0c24633469346c..5d48dfc3e30339f19ce1019232719d00bcca89c0 100644
--- a/Source/bindings/templates/union.h
+++ b/Source/bindings/templates/union.h
@@ -53,7 +53,7 @@ private:
 
 class V8{{container.cpp_class}} final {
 public:
-    static void toImpl(v8::Isolate*, v8::Local<v8::Value>, {{container.cpp_class}}&, ExceptionState&);
+    static bool toImpl(v8::Isolate*, v8::Local<v8::Value>, {{container.cpp_class}}&, ExceptionState&);
 };
 
 v8::Local<v8::Value> toV8(const {{container.cpp_class}}&, v8::Local<v8::Object>, v8::Isolate*);
@@ -73,13 +73,13 @@ struct NativeValueTraits<{{container.cpp_class}}> {
 {% for cpp_type in nullable_cpp_types %}
 class V8{{cpp_type}}OrNull final {
 public:
-    static void toImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8Value, {{cpp_type}}& impl, ExceptionState& exceptionState)
+    static bool toImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8Value, {{cpp_type}}& impl, ExceptionState& exceptionState)
     {
         {# http://heycam.github.io/webidl/#es-union #}
         {# 1. null or undefined #}
         if (isUndefinedOrNull(v8Value))
-            return;
-        V8{{cpp_type}}::toImpl(isolate, v8Value, impl, exceptionState);
+            return true;
+        return V8{{cpp_type}}::toImpl(isolate, v8Value, impl, exceptionState);
     }
 };