Dartium custom element lifecycle event support.

tools/dom/scripts/systemnative.py

Index: tools/dom/scripts/systemnative.py
diff --git a/tools/dom/scripts/systemnative.py b/tools/dom/scripts/systemnative.py
index 2dc7361df3e1d7bb65950ddfa417a2742f808119..cc5b9caf92aa77c40887efc71677a6c252c9f71e 100644
--- a/tools/dom/scripts/systemnative.py
+++ b/tools/dom/scripts/systemnative.py
@@ -734,6 +734,7 @@ class DartiumBackend(HtmlDartGenerator):
     cpp_arguments = []
     runtime_check = None
     raises_exceptions = raises_dom_exception or arguments
+    needs_custom_element_callbacks = False
 
     # TODO(antonm): unify with ScriptState below.
     requires_stack_info = (ext_attrs.get('CallWith') == 'ScriptArguments|ScriptState' or
@@ -785,6 +786,10 @@ class DartiumBackend(HtmlDartGenerator):
     if 'Reflect' in ext_attrs:
       cpp_arguments = [self._GenerateWebCoreReflectionAttributeName(node)]
 
+    if ext_attrs.get('CustomElementCallbacks') == 'Enable':
+      self._cpp_impl_includes.add('"core/dom/CustomElementCallbackDispatcher.h"')
+      needs_custom_element_callbacks = True
+
     if return_type_is_nullable:
       cpp_arguments = ['isNull']
 
@@ -907,6 +912,9 @@ class DartiumBackend(HtmlDartGenerator):
           '            return;\n',
           INDEX=len(arguments) + 1)
 
+    if needs_custom_element_callbacks:
+      body_emitter.Emit('        CustomElementCallbackDispatcher::CallbackDeliveryScope deliveryScope;\n');
+
     # Emit arguments.
     start_index = 1 if needs_receiver else 0
     for i, argument in enumerate(arguments):