Limit document.createEvent to existing events

third_party/WebKit/Source/build/scripts/templates/EventFactory.cpp.tmpl

 {% from 'macros.tmpl' import license %}
 {{license()}}
 
 {% if suffix == 'Modules' %}
 #include "modules/{{namespace}}{{suffix}}Factory.h"
 {% else %}
 #include "core/events/{{namespace}}Factory.h"
 {% endif %}
 
 #include "{{namespace}}{{suffix}}Headers.h"
 #include "core/frame/Deprecation.h"
 #include "platform/RuntimeEnabledFeatures.h"
 
 namespace blink {
 
 {{namespace}}* {{namespace}}{{suffix}}Factory::create(ExecutionContext* executionContext, const String& type)
 {
-    {% for event in events %}
+    {% for event in events if event|script_name|create_event_whitelist or event|script_name|create_event_legacy_whitelist %}
     {% if event|script_name|create_event_whitelist %}
     if (equalIgnoringCase(type, "{{event|script_name}}"){% if event.RuntimeEnabled %} && RuntimeEnabledFeatures::{{event.RuntimeEnabled|lower_first}}(){% endif %}) {
     {% else %}
     if (type == "{{event|script_name}}"{% if event.RuntimeEnabled %} && RuntimeEnabledFeatures::{{event.RuntimeEnabled|lower_first}}(){% endif %}) {
     {% endif %}
         {% if not event|script_name|create_event_whitelist %}
         UseCounter::count(executionContext, UseCounter::{{event|script_name|measure_name}});
         {% endif %}
         return {{event|cpp_name}}::create();
     }
     {% endfor %}
     return nullptr;
 }
 
 } // namespace blink