Introduce infrastructure for tracing ScriptWrappables.

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

 {% include 'copyright_block.txt' %}
 #include "{{v8_class_or_partial}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % cpp_class_or_partial %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace blink {
 {% set to_active_scriptwrappable = '%s::toActiveScriptWrappable' % v8_class
                                    if active_scriptwrappable else '0' %}
@@ skipping 156 matching lines @@
 {% block named_property_setter_callback %}{% endblock %}
 {% block named_property_query %}{% endblock %}
 {% block named_property_query_callback %}{% endblock %}
 {% block named_property_deleter %}{% endblock %}
 {% block named_property_deleter_callback %}{% endblock %}
 {% block named_property_enumerator %}{% endblock %}
 {% block named_property_enumerator_callback %}{% endblock %}
 } // namespace {{cpp_class_or_partial}}V8Internal
 
 {% block visit_dom_wrapper %}{% endblock %}
+{% block trace_wrapper_references %}{% endblock %}
 {##############################################################################}
 {% block install_attributes %}
 {% from 'attributes.cpp' import attribute_configuration with context %}
 {% if has_attribute_configuration %}
 // Suppress warning: global constructors, because AttributeConfiguration is trivial
 // and does not depend on another global objects.
 #if defined(COMPONENT_BUILD) && defined(WIN32) && COMPILER(CLANG)
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wglobal-constructors"
 #endif
@@ skipping 214 matching lines @@
 {{method_implemented_in_private_script(method)}}
 {% endfor %}
 {% for attribute in attributes if attribute.is_implemented_in_private_script %}
 {{attribute_getter_implemented_in_private_script(attribute)}}
 {% if attribute.has_setter %}
 {{attribute_setter_implemented_in_private_script(attribute)}}
 {% endif %}
 {% endfor %}
 {% block partial_interface %}{% endblock %}
 } // namespace blink