DevTools: add console test helpers to new test runner & migrate a console test

third_party/WebKit/LayoutTests/http/tests/inspector/devtools-js/console/console-clear.js

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (async function() {
   TestRunner.addResult("Tests that console is cleared upon requestClearMessages call.\n");
 
   await TestRunner.loadPanel("console");
   await TestRunner.loadModule("console_test_runner");
 
   function log() {
     // Fill console.
     console.log("one");
     console.log("two");
     console.log("three");
   }
 
   await TestRunner.evaluateInPagePromise(`(${log.toString()})()`);
   TestRunner.addResult("=== Before clear ===");
   ConsoleTestRunner.dumpConsoleMessages();
 
   Console.ConsoleView.clearConsole();
   TestRunner.deprecatedRunAfterPendingDispatches(callback);
   function callback() {
     TestRunner.addResult("=== After clear ===");
     ConsoleTestRunner.dumpConsoleMessages();
     TestRunner.completeTest();
   }
 })();