Refactor precacheChildNodes slightly (#8018)

This ‘fixes’ a bizarre IE9 script engine issue. #7803

src/renderers/dom/shared/ReactDOMComponentTree.js

@@ -22,6 +22,18 @@ var Flags = ReactDOMComponentFlags;
 var internalInstanceKey =
   '__reactInternalInstance$' + Math.random().toString(36).slice(2);
 
+/**
+ * Check if a given node should be cached.
+ */
+function shouldPrecacheNode(node, nodeID) {
+  return (node.nodeType === 1 &&
+          node.getAttribute(ATTR_NAME) === String(nodeID)) ||
+         (node.nodeType === 8 &&
+          node.nodeValue === ' react-text: ' + nodeID + ' ') ||
+         (node.nodeType === 8 &&
+          node.nodeValue === ' react-empty: ' + nodeID + ' ');
+}
+
 /**
  * Drill down (through composites and empty components) until we get a host or
  * host text component.
@@ -87,12 +99,7 @@ function precacheChildNodes(inst, node) {
     }
     // We assume the child nodes are in the same order as the child instances.
     for (; childNode !== null; childNode = childNode.nextSibling) {
-      if ((childNode.nodeType === 1 &&
-           childNode.getAttribute(ATTR_NAME) === String(childID)) ||
-          (childNode.nodeType === 8 &&
-           childNode.nodeValue === ' react-text: ' + childID + ' ') ||
-          (childNode.nodeType === 8 &&
-           childNode.nodeValue === ' react-empty: ' + childID + ' ')) {
+      if (shouldPrecacheNode(childNode, childID)) {
         precacheNode(childInst, childNode);
         continue outer;
       }