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

third_party/WebKit/LayoutTests/inspector-protocol/dom/dom-childNodeCount.js

+(async function(testRunner) {
+  var {page, session, dp} = await testRunner.startHTML(`
+        <div id='container' style='display:none'><div>child1</div><div>child2</div></div>
+  `, '');
+  var NodeTracker = await testRunner.loadScript('../resources/node-tracker.js');
+  var nodeTracker = new NodeTracker(dp);
+  var containerNodeId;
+  dp.DOM.onChildNodeCountUpdated(message => {
+    if (message.params.nodeId === containerNodeId)
+      testRunner.log('childCountUpdated: ' + message.params.childNodeCount);
+  });
+  var response = await dp.DOM.getDocument();
+  var message = await dp.DOM.querySelector({nodeId: response.result.root.nodeId, selector: '#container' });
+
+  containerNodeId = message.result.nodeId;
+  testRunner.log('Node arrived with childNodeCount: ' + nodeTracker.nodeForId(containerNodeId).childNodeCount);
+
+  await Promise.all([
+    session.evaluate(addNode),
+    session.evaluate(removeNode),
+    session.evaluate(removeNode),
+    session.evaluate(removeNode),
+  ]);
+  testRunner.completeTest();
+
+  function addNode() {
+    var container = document.getElementById('container');
+    container.appendChild(document.createElement('div'));
+  }
+
+  function removeNode() {
+    var container = document.getElementById('container');
+    container.firstChild.remove();
+  }
+})