Make getComputedStyle throw for incorrect first parameter

Source/core/frame/Window.idl

Index: Source/core/frame/Window.idl
diff --git a/Source/core/frame/Window.idl b/Source/core/frame/Window.idl
index 7a894a405efa961fc75d84b1de8c66460cab61a4..75ecd318881819e2d1095bd322289d395783d65d 100644
--- a/Source/core/frame/Window.idl
+++ b/Source/core/frame/Window.idl
@@ -138,8 +138,8 @@
     readonly attribute StyleMedia styleMedia;
 
     // DOM Level 2 Style Interface
-    CSSStyleDeclaration getComputedStyle([Default=Undefined] optional Element element,
-                                         [TreatUndefinedAs=NullString, Default=Undefined] optional DOMString? pseudoElement);
+    [TypeChecking=Interface]CSSStyleDeclaration getComputedStyle([Default=Undefined] optional Element element,

[tkent, 2014/11/25 22:59:28]

nit: add a space between ']' and 'C'

+                                                                 [TreatUndefinedAs=NullString, Default=Undefined] optional DOMString? pseudoElement);
 
     // WebKit extensions
     [MeasureAs=GetMatchedCSSRules] CSSRuleList getMatchedCSSRules([Default=Undefined] optional Element element,