Replace many [TreatReturnedNullStringAs=Null] with nullable DOMString

Source/core/css/CSSStyleDeclaration.idl

Index: Source/core/css/CSSStyleDeclaration.idl
diff --git a/Source/core/css/CSSStyleDeclaration.idl b/Source/core/css/CSSStyleDeclaration.idl
index 1fc7e9c6abf3ce95ab3d65efe40b3af68a2f0647..0073e9e49801d9096d9c035c9a6b31f11489a11d 100644
--- a/Source/core/css/CSSStyleDeclaration.idl
+++ b/Source/core/css/CSSStyleDeclaration.idl
@@ -23,14 +23,14 @@
     DependentLifetime,
     WillBeGarbageCollected
 ] interface CSSStyleDeclaration {
-             [TreatReturnedNullStringAs=Null, TreatNullAs=NullString, RaisesException=Setter] attribute DOMString        cssText;
+    [RaisesException=Setter] attribute DOMString?       cssText;
 
-    [TreatReturnedNullStringAs=Null] DOMString          getPropertyValue([Default=Undefined] optional DOMString propertyName);
-    [TreatReturnedNullStringAs=Null, RaisesException] DOMString          removeProperty([Default=Undefined] optional DOMString propertyName);
-    [TreatReturnedNullStringAs=Null] DOMString          getPropertyPriority([Default=Undefined] optional DOMString propertyName);
-     [RaisesException] void setProperty([Default=Undefined] optional DOMString propertyName,
-                                    [TreatNullAs=NullString,Default=Undefined] optional DOMString value,
-                                    [TreatNullAs=NullString] optional DOMString priority = null);
+    DOMString?          getPropertyValue([Default=Undefined] optional DOMString propertyName);
+    [RaisesException] DOMString?          removeProperty([Default=Undefined] optional DOMString propertyName);
+    DOMString?          getPropertyPriority([Default=Undefined] optional DOMString propertyName);
+    [RaisesException] void setProperty([Default=Undefined] optional DOMString propertyName,
+                                       [TreatNullAs=NullString,Default=Undefined] optional DOMString value,
+                                       [TreatNullAs=NullString] optional DOMString priority = null);
 
     readonly attribute unsigned long    length;
     getter DOMString          item([Default=Undefined] optional unsigned long index);