Hammerhead internal event listener is called twice

[Dmitry-Ostashev]

What is your Test Scenario?

Record a test with the TestCafe Studio. See https://github.com/DevExpress/testcafe-studio/issues/2541

What is the Current behavior?

Internal event listener may be called twice

What is the Expected behavior?

It should be called once

What is your web application and your TestCafe test code?

Your website URL (or attach your complete example):

Your complete test code (or attach your test files):

fixture `test`
    .page `about:blank`;

test('test', async t => {
    await t.eval(() => {        
        window.counter = 0;
        window['%hammerhead%'].eventSandbox.listeners.addInternalEventListener(window, ["keypress"], () => { 
            window.counter++;
        });
        var ev = new Event('keypress');
        ev.key = 'a';
        window.dispatchEvent(ev);
    });
    await t.wait(1000);
    console.log(await t.eval(() => window.counter));    
});

Steps to Reproduce:

Another way to determine this issue:

1. Set a huge t.wait() timeout in the test above
2. Run test, open chrome DevTools
3. Check the event handlers via console: getEventListeners(window).keypress
4. There will be two same handlers

Your Environment details:

• testcafe version: 1.2.1
• node.js version: 10.15.1
• command-line arguments: testcafe chrome test.js
• browser name and version: Chrome 75, Opera 62
• platform and version: Windows 10, Linux Ubuntu 18.04

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