Made Text#assignedSlot and Element#assignedSlot nullable.

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

Index: third_party/WebKit/Source/core/dom/Text.idl
diff --git a/third_party/WebKit/Source/core/dom/Text.idl b/third_party/WebKit/Source/core/dom/Text.idl
index 74cfdac6547a9a43ccf3bf0a9e1e1ff4aa6c7687..c4a6c6343e5a0c20da8aa9600c1cdc61956fb2d2 100644
--- a/third_party/WebKit/Source/core/dom/Text.idl
+++ b/third_party/WebKit/Source/core/dom/Text.idl
@@ -26,8 +26,9 @@
     [NewObject, DoNotTestNewObject, RaisesException] Text splitText(unsigned long offset);
     [MeasureAs=TextWholeText] readonly attribute DOMString wholeText;
 
-    // Shadow DOM
-    // https://w3c.github.io/webcomponents/spec/shadow/#extensions-to-text-interface
+    // Mixin Slotable
+    // https://dom.spec.whatwg.org/#mixin-slotable
+    [ImplementedAs=assignedSlotForBinding] readonly attribute HTMLSlotElement? assignedSlot;
+
     NodeList getDestinationInsertionPoints();

[foolip, 2016/12/12 11:33:48]

Add back Shadow DOM + link

-    [ImplementedAs=assignedSlotForBinding] readonly attribute HTMLSlotElement assignedSlot;
 };