Have bindings layer assume and insist that all interface types are GCed.

third_party/WebKit/Source/bindings/templates/attributes.cpp

 {% from 'utilities.cpp' import declare_enum_validation_variable, v8_value_to_local_cpp_value, check_origin_trial %}
 
 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_data_type_property %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- endif %})
@@ skipping 89 matching lines @@
         v8SetReturnValueNull(info);
         return;
     }
     {% endif %}
     {% if attribute.cached_attribute_validation_method %}
     v8::Local<v8::Value> v8Value({{attribute.cpp_value_to_v8_value}});
     V8HiddenValue::setHiddenValue(ScriptState::current(info.GetIsolate()), holder, propertyName, v8Value);
     {% endif %}
     {# v8SetReturnValue #}
     {% if attribute.is_keep_alive_for_gc %}
-    if ({{attribute.cpp_value}} && DOMDataStore::setReturnValue{{world_suffix}}(info.GetReturnValue(), {{attribute.cpp_value}}.get()))
+    if ({{attribute.cpp_value}} && DOMDataStore::setReturnValue{{world_suffix}}(info.GetReturnValue(), {{attribute.cpp_value}}))
         return;
-    v8::Local<v8::Value> v8Value(toV8({{attribute.cpp_value}}.get(), holder, info.GetIsolate()));
+    v8::Local<v8::Value> v8Value(toV8({{attribute.cpp_value}}, holder, info.GetIsolate()));
     if (!v8Value.IsEmpty()) {
         V8HiddenValue::setHiddenValue(ScriptState::current(info.GetIsolate()), holder, v8AtomicString(info.GetIsolate(), "{{attribute.name}}"), v8Value);
         {{attribute.v8_set_return_value}};
     }
     {% elif world_suffix %}
     {{attribute.v8_set_return_value_for_main_world}};
     {% else %}
     {% if attribute.use_output_parameter_for_result %}
     {{attribute.cpp_type}} result;
     {{attribute.cpp_value}};
@@ skipping 376 matching lines @@
        setter_callback_for_main_world,
        wrapper_type_info,
        access_control,
        property_attribute,
        only_exposed_to_private_script,
        property_location(attribute),
        holder_check,
    ] %}
 {{'{'}}{{attribute_configuration_list | join(', ')}}{{'}'}}
 {%- endmacro %}