DevTools: migrate inspector-protocol/dom tests to a new test runner

third_party/WebKit/LayoutTests/inspector-protocol/resources/dom-helper.js

+(class DOMHelper {
+  static attributes(node) {
+    var attr = new Map();
+    if (!node.attributes)
+      return attr;
+    for (var i = 0; i < node.attributes.length; i += 2)
+      attr.set(node.attributes[i], node.attributes[i + 1]);
+    return attr;
+  }
+})