DevTools: Fix a bug where user agent shadow dom elements were inspectable

by recursively checking for shadow dom

BUG=582317

Review-Url: https://codereview.chromium.org/2101143002
Cr-Commit-Position: refs/heads/master@{#403359}

third_party/WebKit/Source/devtools/front_end/elements/ElementsPanel.js

@@ -868,8 +868,10 @@ WebInspector.ElementsPanel.prototype = {
      */
     _leaveUserAgentShadowDOM: function(node)
     {
-        var userAgentShadowRoot = node.ancestorUserAgentShadowRoot();
-        return userAgentShadowRoot ? /** @type {!WebInspector.DOMNode} */ (userAgentShadowRoot.parentNode) : node;
+        var userAgentShadowRoot;
+        while ((userAgentShadowRoot = node.ancestorUserAgentShadowRoot()) && userAgentShadowRoot.parentNode)
+            node = userAgentShadowRoot.parentNode;
+        return node;
     },
 
     /**