safeDialogs option is broken since 7.0.0 (up to 9.0.0-beta.2, at least)

[ChALkeR]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Issue Details

• Electron Version:
  • 9.0.0-beta.2
  • 8.0.1
  • 7.1.13
  • 7.0.0
• Operating System:
  • Linux xps 5.5.4-arch1-1 #1 SMP PREEMPT Sat, 15 Feb 2020 00:36:29 +0000 x86_64 GNU/Linux (Arch Linux current)
  • macOS 10.15.3
• Last Known Working Electron version:
  • 6.1.8 -- fine, not affected

Expected Behavior

• When safeDialogs option is used, I expect to see a "Prevent this app from creating additional dialogs" checkbox on all alerts after the first one, like it happened in Electron 6.1.8.
• I expect safeDialogs option to do at least something.

Basically, how 6.x behaves.

Actual Behavior

• That checkbox does not appear on second alert, or on any other subsequent alert (tried about 10).
• There seems to no observable difference at all between turning that option on or off.

To Reproduce

const { BrowserWindow, app } = require('electron')
app.on('ready', () => {
  const window = new BrowserWindow({
    webPreferences: {
      //partition: 'memory',
      safeDialogs: true,
    }
  })
  window.webContents.loadURL('about:blank') // also could be e.g. https://example.com/
  window.webContents.on('did-finish-load', () => {
    window.webContents.executeJavaScript(`
      document.body.innerText = window.navigator.userAgent // (not required)
      alert(0)
      setTimeout(() => { alert(1) }, 100) // timeout for UA to be shown
    `)
  })
  window.show()
})

Screenshots

v6.1.8 (correct behavior)

v7.0.0

v7.1.13

v8.0.1

9.0.0-beta.2

Additional Information

• Documented here: https://www.electronjs.org/docs/api/browser-window#new-browserwindowoptions
• This does not seem to be a duplicate of closed safeDialogs option doesn't work #17543, as this affects only versions starting from v7.0.0.
• This does not seem to be a problem of specific configuration/url/scheme/whatever -- I was not able to make that option work on a recent Electron version with any attempted configuration.

[ChALkeR]

I can confirm this now works on master, thanks!