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

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

Index: third_party/WebKit/LayoutTests/external/wpt/selection/common.js
diff --git a/third_party/WebKit/LayoutTests/external/wpt/selection/common.js b/third_party/WebKit/LayoutTests/external/wpt/selection/common.js
index 4b37c2632c2cc19d8b47eb0486cf78e2fb641cd9..51579e42444e3c723ed9c80283887d163bfd150d 100644
--- a/third_party/WebKit/LayoutTests/external/wpt/selection/common.js
+++ b/third_party/WebKit/LayoutTests/external/wpt/selection/common.js
@@ -977,3 +977,14 @@ function assertSelectionNoChange(func) {
          "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);
+}