Made Text#assignedSlot and Element#assignedSlot nullable.

third_party/WebKit/Source/core/dom/Element.idl

 /*
  * Copyright (C) 2006, 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 16 matching lines @@
 
 interface Element : Node {
     readonly attribute DOMString? namespaceURI;
     readonly attribute DOMString? prefix;
     readonly attribute DOMString localName;
     readonly attribute DOMString tagName;
 
     [CEReactions, Reflect] attribute DOMString id;
     [CEReactions, Reflect=class] attribute DOMString className;
     [SameObject, CEReactions, PerWorldBindings, PutForwards=value] readonly attribute DOMTokenList classList;
+    [Unscopable, CEReactions, Reflect] attribute DOMString slot;
 
     // PointerEvent
     //https://www.w3.org/TR/pointerevents/#extensions-to-the-element-interface
     [RuntimeEnabled=PointerEvent, RaisesException] void setPointerCapture (long pointerId);
     [RuntimeEnabled=PointerEvent, RaisesException] void releasePointerCapture (long pointerId);
     [RuntimeEnabled=PointerEvent] attribute EventHandler ongotpointercapture;
     [RuntimeEnabled=PointerEvent] attribute EventHandler onlostpointercapture;
 
     // PointerEvent v2
     // https://w3c.github.io/pointerevents/#extensions-to-the-element-interface
@@ skipping 13 matching lines @@
     Attr? getAttributeNode(DOMString name);
     Attr? getAttributeNodeNS(DOMString? namespaceURI, DOMString localName);
     [RaisesException, CEReactions, CustomElementCallbacks] Attr? setAttributeNode(Attr attr);
     [RaisesException, CEReactions, CustomElementCallbacks] Attr? setAttributeNodeNS(Attr attr);
     [RaisesException, CEReactions, CustomElementCallbacks] Attr removeAttributeNode(Attr attr);
 
     [RaisesException] Element? closest(DOMString selectors);
     [RaisesException] boolean matches(DOMString selectors);
     [RaisesException, ImplementedAs=matches, MeasureAs=ElementPrefixedMatchesSelector] boolean webkitMatchesSelector(DOMString selectors); // historical alias of .matches
 
+    [RaisesException, CallWith=ScriptState, MeasureAs=ElementAttachShadow] ShadowRoot attachShadow(ShadowRootInit shadowRootInitDict);
+    [PerWorldBindings, ImplementedAs=openShadowRoot] readonly attribute ShadowRoot? shadowRoot;
+
     HTMLCollection getElementsByTagName(DOMString localName);
     HTMLCollection getElementsByTagNameNS(DOMString? namespaceURI, DOMString localName);
     HTMLCollection getElementsByClassName(DOMString classNames);
 
     [RaisesException, CEReactions, CustomElementCallbacks] Element? insertAdjacentElement(DOMString where, Element element);
     [RaisesException] void insertAdjacentText(DOMString where, DOMString data);
 
+    // Mixin Slotable
+    // https://dom.spec.whatwg.org/#mixin-slotable
+    [ImplementedAs=assignedSlotForBinding] readonly attribute HTMLSlotElement? assignedSlot;
+
     // DOM Parsing and Serialization
     // https://dvcs.w3.org/hg/innerhtml/raw-file/tip/index.html#extensions-to-the-element-interface
     [TreatNullAs=NullString, CEReactions, CustomElementCallbacks, RaisesException=Setter] attribute DOMString innerHTML;
     [TreatNullAs=NullString, CEReactions, CustomElementCallbacks, RaisesException=Setter] attribute DOMString outerHTML;
     [CEReactions, CustomElementCallbacks, RaisesException] void insertAdjacentHTML(DOMString position, DOMString text);
 
     // Shadow DOM
     // https://w3c.github.io/webcomponents/spec/shadow/#extensions-to-element-interface
     [RaisesException, CallWith=ScriptState, MeasureAs=ElementCreateShadowRoot] ShadowRoot createShadowRoot();
-    [RaisesException, CallWith=ScriptState, MeasureAs=ElementAttachShadow] ShadowRoot attachShadow(ShadowRootInit shadowRootInitDict);
     NodeList getDestinationInsertionPoints();
-    [PerWorldBindings, ImplementedAs=openShadowRoot] readonly attribute ShadowRoot? shadowRoot;
-    [Unscopable, CEReactions, Reflect] attribute DOMString slot;
-    [ImplementedAs=assignedSlotForBinding] readonly attribute HTMLSlotElement assignedSlot;
+
 
     // Pointer Lock
     // https://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html#extensions-to-the-element-interface
     [MeasureAs=ElementRequestPointerLock] void requestPointerLock();
 
     // CSSOM View Module
     // https://dev.w3.org/csswg/cssom-view/#extension-to-the-element-interface
     // FIXME: getClientRect() and getBoundingClientRect() should
     // return DOMRectList and DOMRect respectively.
     ClientRectList getClientRects();
@@ skipping 34 matching lines @@
     attribute EventHandler oncut;
     attribute EventHandler onpaste;
     attribute EventHandler onsearch;
     attribute EventHandler onselectstart;
     attribute EventHandler onwheel;
 };
 
 Element implements ParentNode;
 Element implements ChildNode;
 Element implements NonDocumentTypeChildNode;