selection: Do not run invalid sub-tests with unselectable Range.

third_party/WebKit/LayoutTests/external/wpt/selection/common.js

 "use strict";
 // TODO: iframes, contenteditable/designMode
 
 // Everything is done in functions in this test harness, so we have to declare
 // all the variables before use to make sure they can be reused.
 var selection;
 var testDiv, paras, detachedDiv, detachedPara1, detachedPara2,
     foreignDoc, foreignPara1, foreignPara2, xmlDoc, xmlElement,
     detachedXmlElement, detachedTextNode, foreignTextNode,
     detachedForeignTextNode, xmlTextNode, detachedXmlTextNode,
@@ skipping 959 matching lines @@
     func();
 
     assert_equals(selection.rangeCount, originalCount,
         "The operation should not add Range");
     if (originalCount < 1)
         return;
     assert_equals(selection.getRangeAt(0), originalRange,
          "The operation should not replace a registered Range");
 }
 
+/**
+ * Check if the specified node can be selectable with window.getSelection()
+ * methods.
+ */
+function isSelectableNode(node) {
+    if (!node)
+        return false;
+    if (node.nodeType == Node.DOCUMENT_TYPE_NODE)
+        return false;
+    return document.contains(node);
+}