[Bindings] Replace void cast with ALLOW_UNUSED_LOCAL in dictionary_v8.cpp.tmpl.

third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl

Index: third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl
diff --git a/third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl b/third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl
index 7e78fbd48104d6fea6d9c23cef9f2a0271d05455..bf6096e026e0b8dfe7d1f006a56f0b80a2891bb4 100644
--- a/third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl
+++ b/third_party/WebKit/Source/bindings/templates/dictionary_v8.cpp.tmpl
@@ -28,7 +28,7 @@ void {{v8_class}}::toImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8Value, {{
     {% endif %}
   }
   v8::Local<v8::Object> v8Object = v8Value.As<v8::Object>();
-  (void)v8Object;
+  ALLOW_UNUSED_LOCAL(v8Object);
 
   {% if parent_v8_class %}
   {{parent_v8_class}}::toImpl(isolate, v8Value, impl, exceptionState);