Allow positional selectors to match elements without a parent.

third_party/WebKit/LayoutTests/http/tests/misc/acid3.html

Index: third_party/WebKit/LayoutTests/http/tests/misc/acid3.html
diff --git a/third_party/WebKit/LayoutTests/http/tests/misc/acid3.html b/third_party/WebKit/LayoutTests/http/tests/misc/acid3.html
index f9cdc4c44c245427af3467d0f775023325120310..568fb543d457bbb71147e2634c40f9620e666423 100644
--- a/third_party/WebKit/LayoutTests/http/tests/misc/acid3.html
+++ b/third_party/WebKit/LayoutTests/http/tests/misc/acid3.html
@@ -1261,7 +1261,7 @@
         var p1 = doc.createElement("p");
         doc.body.appendChild(doc.createTextNode(" TEST "));
         doc.body.appendChild(p1);
-        expect(doc.documentElement, notFirst, "root element, with no parent node, claims to be a :first-child");
+        expect(doc.documentElement, first, "root element, with no parent node, claims to be a :first-child");
         expect(doc.documentElement.firstChild, first, "first child of root node didn't match :first-child");
         expect(doc.documentElement.firstChild.firstChild, first, "failure 3");
         expect(doc.body, notFirst, "failure 4");