Make Event.path() return a pre-calculated NodeList rather than calculating it dynamically.

LayoutTests/fast/dom/shadow/event-path-with-dom-mutation.html

Index: LayoutTests/fast/dom/shadow/event-path-with-dom-mutation.html
diff --git a/LayoutTests/fast/dom/shadow/event-path-in-shadow-tree.html b/LayoutTests/fast/dom/shadow/event-path-with-dom-mutation.html
similarity index 88%
copy from LayoutTests/fast/dom/shadow/event-path-in-shadow-tree.html
copy to LayoutTests/fast/dom/shadow/event-path-with-dom-mutation.html
index 398218d9697978fd5edcb9e6add40527d3e45c9e..387882732171a2a3ccaf8fe5966545eecf2ce1b4 100644
--- a/LayoutTests/fast/dom/shadow/event-path-in-shadow-tree.html
+++ b/LayoutTests/fast/dom/shadow/event-path-with-dom-mutation.html
@@ -34,6 +34,13 @@ sandbox.appendChild(
         debug(dumpNodeList(event.path()));
     });
 });
+['B', 'A/E/I'].forEach(function(path) {
+    getNodeInShadowTreeStack(path).addEventListener('click', function(event) {
+        debug('\nRemoving node ' + dumpNode(event.currentTarget.firstChild));
+        event.currentTarget.removeChild(event.currentTarget.firstChild);
+    });
+});
+
 var clickEvent = document.createEvent("MouseEvents");
 clickEvent.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
 document.getElementById('C').dispatchEvent(clickEvent);