V8DOMConfiguration.cpp [1] is responsible for installing methods, accessors, etc.  Creating new FunctionTemplates has v8::ConstructorBehavior::kAllow as the default ConstructorBehavior.  This likely should be stricter, and we should pass kThrow for any non-constructor method.

[1] https://cs.chromium.org/chromium/src/third_party/WebKit/Source/bindings/core/v8/V8DOMConfiguration.cpp?q=v8domconfiguration.cpp&sq=package:chromium&dr