[DevTools] New harness for inspector-protocol layout tests

third_party/WebKit/LayoutTests/inspector-protocol/page/javascriptDialogEvents.js

+(async function(testRunner) {
+  let {page, session, dp} = await testRunner.startBlank('');
+
+  await session.evaluate(`
+    testRunner.setShouldStayOnPageAfterHandlingBeforeUnload(true);
+
+    // JavaScript onbeforeunload dialogs require a user gesture.
+    if (window.eventSender) {
+        eventSender.mouseMoveTo(5, 5);
+        eventSender.mouseDown();
+        eventSender.mouseUp();
+    }
+
+    function onBeforeUnload()
+    {
+        window.removeEventListener('beforeunload', onBeforeUnload);
+        return 'beforeunload in javascriptDialogEvents';
+    }
+    window.onbeforeunload = onBeforeUnload;
+  `);
+
+  dp.Page.onJavascriptDialogOpening(event => {
+    testRunner.log('Opening dialog: type=' + event.params.type + '; message=' + event.params.message);
+  });
+  dp.Page.onJavascriptDialogClosed(event => {
+    testRunner.log('Closed dialog: result=' + event.params.result);
+  });
+
+  dp.Page.enable();
+  dp.Page.navigate({url: 'http://nosuchurl' });
+  await session.evaluate('alert("alert")');
+  await session.evaluate('confirm("confirm")');
+  await session.evaluate('prompt("prompt")');
+  testRunner.completeTest();
+})