### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

13.0.0-beta.20

### What operating system are you using?

macOS

### Operating System Version

11.3.1

### What arch are you using?

arm64 (including Apple Silicon)

### Last Known Working Electron version

_No response_

### Expected Behavior

Naturally, the window's borders should be rounded, with nothing obscure protruding amongst them--And they should stay that way _after_ maximization, like so:
![Screen Shot 2021-05-07 at 2 48 02 PM](https://user-images.githubusercontent.com/83843298/117511979-8d1ba180-af43-11eb-99f6-5163877619f4.png)


### Actual Behavior

But, for some weird reason, after (and while) the window is maximized, weird looking white corners appear on every point of the window's border radius...
![Screen Shot 2021-05-07 at 2 49 47 PM](https://user-images.githubusercontent.com/83843298/117512201-074c2600-af44-11eb-9f20-3017207cbea5.png)


### Testcase Gist URL

https://gist.github.com/TurnipTotSoftware/74db97bee9b29183006fd1204cfff746

### Additional Information

This glitch also happens after my Mac sleeps for a bit...
Hopefully this problem is an easy fix!

Good day👍
shell/browser/native_window_mac.h
void SetFullScreenTransitionState(FullScreenTransitionState state);
  void HandlePendingFullscreenTransitions();
  enum class VisualEffectState {
    kFollowWindow,
    kActive,
    kInactive,
  };
  enum class TitleBarStyle {
    kNormal,
    kHidden,
    kHiddenInset,
    kCustomButtonsOnHover,
  };
  TitleBarStyle title_bar_style() const { return title_bar_style_; }
  ElectronPreviewItem* preview_item() const { return preview_item_.get(); }
  ElectronTouchBar* touch_bar() const { return touch_bar_.get(); }
  bool zoom_to_page_width() const { return zoom_to_page_width_; }
  bool always_simple_fullscreen() const { return always_simple_fullscreen_; }
 protected:
  
  bool CanResize() const override;
  views::View* GetContentsView() override;
  
  void OnNativeThemeUpdated(ui::NativeTheme* observed_theme) override;
  
  void OnDisplayMetricsChanged(const display::Display& display,