Add "WebDriver BiDi network is offline" hook

Author: sadym-chromium

index.bs

@@ -9472,6 +9472,23 @@ and |user context| are:
 
 </div>
 
+<div algorithm>
+The <dfn export>WebDriver BiDi network is offline</dfn> steps given
+[=environment settings object=] |settings| are:
+
+1. Let |navigable| be |settings|'s [=relevant global object=]'s
+   <a>associated <code>Document</code></a>'s [=/node navigable=].
+
+1. Let |emulated network conditions| be the result of
+   [=get emulated network conditions=] with [|navigable|].
+
+1. If |emulated network conditions| is not null and |emulated network conditions|'s
+   [=emulated-network-conditions-struct/offline=] is true, return true.
+
+1. Return false.
+
+</div>
+
 <div algorithm>
 The steps to <dfn>get emulated network conditions</dfn> given |related navigables|
 are: