Write out unique includes in element factories

Source/build/scripts/templates/ElementFactory.cpp.tmpl

 {% from "macros.tmpl" import license %}
 {{ license() }}
 
 #include "config.h"
 #include "{{namespace}}ElementFactory.h"
 
 #include "{{namespace}}Names.h"
-{% for tag in tags|sort %}
-#include "core/{{namespace|lower}}/{{tag.interface}}.h"
+{% for tag in tags|groupby('interface') %}
+#include "core/{{namespace|lower}}/{{tag[0]}}.h"
 {% endfor %}
 {% if fallback_interface %}
 #include "core/{{namespace|lower}}/{{fallback_interface}}.h"
 {% endif %}
 #include "core/dom/custom/CustomElement.h"
 #include "core/dom/custom/CustomElementRegistrationContext.h"
 #include "core/dom/Document.h"
 #include "core/frame/Settings.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "wtf/HashMap.h"
@@ skipping 74 matching lines @@
     if (document.registrationContext() && CustomElement::isValidName(localName)) {
         RefPtrWillBeRawPtr<Element> element = document.registrationContext()->createCustomTagElement(document, QualifiedName(nullAtom, localName, {{namespace_prefix}}NamespaceURI));
         ASSERT_WITH_SECURITY_IMPLICATION(element->is{{namespace}}Element());
         return static_pointer_cast<{{namespace}}Element>(element.release());
     }
 
     return {{fallback_interface}}::create(QualifiedName(nullAtom, localName, {{namespace_prefix}}NamespaceURI), document);
 }
 
 } // namespace blink