Import dom/ from web-platform-tests

third_party/WebKit/LayoutTests/imported/web-platform-tests/dom/traversal/traversal-support.js

+// |expected| should be an object indicating the expected type of node.
+function assert_node(actual, expected)
+{
+    assert_true(actual instanceof expected.type,
+                'Node type mismatch: actual = ' + actual.nodeType + ', expected = ' + expected.nodeType);
+    if (typeof(expected.id) !== 'undefined')
+        assert_equals(actual.id, expected.id);
+    if (typeof(expected.nodeValue) !== 'undefined')
+        assert_equals(actual.nodeValue, expected.nodeValue);
+}