Window with customButtonsOnHover crashes

[gunta]

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:
  • v9.0.0-beta.12
• Operating System:
  • macOS 10.15.4

Expected Behavior

Don't crash

Actual Behavior

It crashes when entering fullscreen.

To Reproduce

Works OK

const mainWindow = new BrowserWindow({
    titleBarStyle: 'hidden',
});

Crashes

const mainWindow = new BrowserWindow({
    titleBarStyle: 'customButtonsOnHover',
});

Additional Information

When starting the app, this is the log

(node:5588) UnhandledPromiseRejectionWarning: Error: Script failed to execute, this normally means an error was thrown. Check the renderer console for the error.
    at WebFrame../lib/renderer/api/web-frame.ts.WebFrame.<computed> [as executeJavaScript] (electron/js2c/renderer_init.js:1590:33)
    at electron/js2c/renderer_init.js:2844:43
    at EventEmitter.<anonymous> (electron/js2c/renderer_init.js:2419:57)
    at EventEmitter.emit (events.js:210:5)
    at Object.onMessage (electron/js2c/renderer_init.js:2188:16)
(node:5588) UnhandledPromiseRejectionWarning: Error: Script failed to execute, this normally means an error was thrown. Check the renderer console for the error.
    at WebFrame../lib/renderer/api/web-frame.ts.WebFrame.<computed> [as executeJavaScript] (electron/js2c/renderer_init.js:1590:33)
    at electron/js2c/renderer_init.js:2844:43
    at EventEmitter.<anonymous> (electron/js2c/renderer_init.js:2419:57)
    at EventEmitter.emit (events.js:210:5)
    at Object.onMessage (electron/js2c/renderer_init.js:2188:16)
(node:5588) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:5588) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:5588) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:5588) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

And when crashing this is the log

2020-04-05 20:17:59.822 Electron[5588:60708] *** Assertion failure in -[ElectronNSWindow titlebarAccessoryViewControllers], /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/AppKit/AppKit-1894.40.150/AppKit.subproj/NSWindow.m:3337

Not sure, but #15704 may be related.

[codebytere]

We used to see this problem, but i'm not able to repro it using this fiddle anymore. I was able to click 'Toggle Fullscreen' in the menu bar with no issue repeatedly. Does the same happen for you?