Drop support for [TreatUndefinedAs=NullString]

third_party/WebKit/Source/core/frame/Window.idl

Index: third_party/WebKit/Source/core/frame/Window.idl
diff --git a/third_party/WebKit/Source/core/frame/Window.idl b/third_party/WebKit/Source/core/frame/Window.idl
index 0dfdb5338f70f667c4f533b3303fe6f6a068a08b..2152614b762bbfd80b45ac0f7dc0d7c23c80bdde 100644
--- a/third_party/WebKit/Source/core/frame/Window.idl
+++ b/third_party/WebKit/Source/core/frame/Window.idl
@@ -167,7 +167,7 @@
     [MeasureAs=WindowDefaultstatus, ImplementedAs=defaultStatus] attribute DOMString defaultstatus;
     [MeasureAs=StyleMedia] readonly attribute StyleMedia styleMedia;
     [DeprecateAs=GetMatchedCSSRules, LegacyInterfaceTypeChecking] CSSRuleList getMatchedCSSRules([Default=Undefined] optional Element element,
-                                                                                                 [TreatUndefinedAs=NullString, Default=Undefined] optional DOMString? pseudoElement);
+                                                                                                 [Default=Undefined] optional DOMString? pseudoElement);
     // This is the interface orientation in degrees. Some examples are:
     //  0 is straight up; -90 is when the device is rotated 90 clockwise;
     //  90 is when rotated counter clockwise.