selection: Align collapse-NN.html and extend-NN.html to the latest draft.

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 85375d5723adceb037e7ce977a34c286fd96f7a4..4b37c2632c2cc19d8b47eb0486cf78e2fb641cd9 100644
--- a/third_party/WebKit/LayoutTests/external/wpt/selection/common.js
+++ b/third_party/WebKit/LayoutTests/external/wpt/selection/common.js
@@ -958,3 +958,22 @@ function setSelectionBackwards(endpoints) {
         selection.extend(endpoints[0], endpoints[1]);
     }
 }
+
+/**
+ * Verify that the specified func doesn't change the selection.
+ * This function should be used in testharness tests.
+ */
+function assertSelectionNoChange(func) {
+    var originalCount = getSelection().rangeCount;
+    var originalRange = originalCount == 0 ? null : selection.getRangeAt(0);
+
+    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");
+}
+