Use current settings object in content document definition

Since this is a same origin-domain check, we can use any settings
object, as they are all same origin-domain. Part of whatwg#1430.

source

@@ -77026,7 +77026,7 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
    <li><p>Let <var>document</var> be <var>context</var>'s <span>active document</span>.</p></li>
 
    <li><p>If <var>document</var>'s <span>origin</span> and the <span>origin</span> specified by the
-   <span>incumbent settings object</span> are not <span>same origin-domain</span>, then return
+   <span>current settings object</span> are not <span>same origin-domain</span>, then return
    null.</p></li>
 
    <li><p>Return <var>document</var>.</p></li>