Add hasFocus field to ClientWindowInfo

index.bs

@@ -2232,6 +2232,7 @@ browser.ClientWindowInfo = {
   height: js-uint,
   x: js-int,
   y: js-int,
+  hasFocus: bool,
 }
 </pre>
 
@@ -2245,14 +2246,23 @@ To <dfn>get the client window info</dfn> given |client window|:
 
 1. Let |state| be [=get the client window state=] with |client window|.
 
+1. Let |has system focus| be false.
+
+1. For each [=/top-level traversable=] |traversable|:
+
+  1. If |traversable|'s [=client window=] is not |window| then continue.
+
+  1. If |traversable| has [=system focus=], set |has system focus| to true and break.
+
 1. Let |client window info| be a [=/map=] matching the
    <code>browser.ClientWindowsInfo</code> production with the
    <code>clientWindow</code> field set to |client window id|, <code>state</code>
    field set to |state|, the <code>x</code> field set to |client window|'s
    [=client window/x-coordinate=], the <code>y</code> field set to |client
    window|'s [=client window/y-coordinate=], the <code>width</code> field set to
-   |client window|'s [=client window/width=], and the <code>height</code> field
-   set to |client window|'s [=client window/height=].
+   |client window|'s [=client window/width=], the <code>height</code> field
+   set to |client window|'s [=client window/height=], and the
+   <code>hasFocus</code> field set to |has system focus|.
 
 1. Return |client window info|