Make item getter and nameditem getter return nullable in Plugin and PluginArray

third_party/WebKit/Source/modules/plugins/Plugin.idl

Index: third_party/WebKit/Source/modules/plugins/Plugin.idl
diff --git a/third_party/WebKit/Source/modules/plugins/Plugin.idl b/third_party/WebKit/Source/modules/plugins/Plugin.idl
index 6f0b0461f3c8a9c0dfe50ce52e0e97f350365d36..f8db9816fe2f1583fd1c1f6090767385c957780a 100644
--- a/third_party/WebKit/Source/modules/plugins/Plugin.idl
+++ b/third_party/WebKit/Source/modules/plugins/Plugin.idl
@@ -18,6 +18,8 @@
     Boston, MA 02110-1301, USA.
 */
 
+// https://html.spec.whatwg.org/multipage/webappapis.html#plugins-2
+
 [
     ImplementedAs=DOMPlugin
 ] interface Plugin {
@@ -25,7 +27,7 @@
     readonly attribute DOMString filename;
     readonly attribute DOMString description;
     readonly attribute unsigned long length;
-    getter MimeType item([Default=Undefined] optional unsigned long index);
-    MimeType namedItem([Default=Undefined] optional DOMString name);
+    getter MimeType? item([Default=Undefined] optional unsigned long index);
+    MimeType? namedItem([Default=Undefined] optional DOMString name);
     [NotEnumerable, ImplementedAs=namedItem] getter MimeType ([Default=Undefined] optional DOMString name);
 };