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

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

+(async function(testRunner) {
+  var {page, session, dp} = await testRunner.startHTML(`
+    <input></input>
+    <input id='second'></input>
+  `, '');
+
+  testRunner.log(await session.evaluate(getActiveElement));
+  var document = (await dp.DOM.getDocument()).result.root;
+  var node = (await dp.DOM.querySelector({nodeId: document.nodeId, selector: '#second'})).result;
+  await dp.DOM.focus({nodeId: node.nodeId});
+  testRunner.log(await session.evaluate(getActiveElement));
+  testRunner.completeTest();
+
+  function getActiveElement() {
+    var el = document.activeElement;
+    return el ? (el.id || el.tagName) : '(none)';
+  }
+})
+