Emitting CustomElementCallbackDispatcher for all APIs impacting custom element lifecycle

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 84f1cbc1e1d8de0fc0e2895497bda556222b982f..038825c60331ff7c517d43e90bc72947f67d7cb0 100644
--- a/tools/dom/scripts/systemnative.py
+++ b/tools/dom/scripts/systemnative.py
@@ -737,6 +737,7 @@ 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
@@ -791,6 +792,10 @@ class DartiumBackend(HtmlDartGenerator):
     if return_type_is_nullable:
       cpp_arguments = ['isNull']
 
+    if ext_attrs.get('CustomElementCallbacks') == 'Enable':
+      self._cpp_impl_includes.add('"core/dom/CustomElementCallbackDispatcher.h"')
+      needs_custom_element_callbacks = True
+
     v8EnabledPerContext = ext_attrs.get('synthesizedV8EnabledPerContext', ext_attrs.get('V8EnabledPerContext'))
     v8EnabledAtRuntime = ext_attrs.get('synthesizedV8EnabledAtRuntime', ext_attrs.get('V8EnabledAtRuntime'))
     assert(not (v8EnabledPerContext and v8EnabledAtRuntime))
@@ -910,6 +915,9 @@ 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):