[DevTools] New harness for inspector-protocol layout tests

third_party/WebKit/LayoutTests/inspector-protocol/loading-iframe-document-node.js

+(async function(testRunner) {
+  let {page, session, dp} = await testRunner.startBlank('Testing that the Node ID can be retrieved before the onload event is triggered');
+    /*
+     1. Create an iframe and point it to a page with a debugger statement.
+     2. Wait until the debugger statement is hit and pause using the inspector protocol.
+     3. Use the JS context to identify the 'window.document' object inside the iframe.
+     4. Use the JS object to retrieve the DOM agent nodeId for the document node.
+     */
+  dp.Page.onLoadEventFired(() => {
+    // We should finish the test before this event is triggered.
+    // If you see this in the output, then the slow-image is not loaded correctly in the iframe.
+    testRunner.log('FAIL: Iframe load event fired before the test finished.');
+    testRunner.completeTest();
+  });
+  testRunner.log('step1_bootstrap');
+  // Enable Page agent for the Page.loadEventFired event.
+  dp.Page.enable();
+  // Make sure the debugger ready to break on the 'debugger' statement.
+  dp.Debugger.enable();
+  await dp.DOM.getDocument();
+  testRunner.log('Adding iframe');
+  session.evaluate(`
+    var frame = document.createElement('iframe');
+    frame.src = 'data:text/html,<script>debugger;</script>';
+    document.body.appendChild(frame);
+  `);
+  var response = await dp.Debugger.oncePaused();
+  testRunner.log('Paused on the debugger statement');
+  response = await dp.Runtime.callFunctionOn({
+    objectId: response.params.callFrames[0].this.objectId,
+    functionDeclaration: 'function() { return this.document; }'
+  });
+  var objectId = response.result.result.objectId;
+  testRunner.log('step2_requestNode: Requesting DOM node for iframe\'s document node');
+  response = await dp.DOM.requestNode({objectId: objectId});
+  testRunner.log(response.result.nodeId ? 'PASS: Received node for iframe\'s document node' : 'FAIL: Iframe\'s document node is not available');
+  await dp.Debugger.resume();
+  testRunner.log('Test finished');
+  testRunner.completeTest();
+})