Windows - Keyboard does not work with submenus

[bsclifton]

Did you search for similar issues before submitting this one?
Yes

Describe the issue you encountered:
With the new custom rendered titlebar on Windows, you can control the menu using the keyboard (unlike the default electron behavior). You can expand and navigate the menus using the arrow keys, but unfortunately you can't expand submenus.

Expected behavior:
For areas where there are submenus (ex: bookmarks w/ folders), you should be able to navigate into those submenus using the left/right arrow keys

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Windows (all)
• Brave Version:
  HEAD on master
• Steps to reproduce:
  1. Launch Brave
  2. Create a folder in your bookmarks toolbar
  3. Add one bookmark to that new folder
  4. Press ALT to show menu
  5. Use arrow keys to navigate over to Bookmarks menu and hit down
  6. Scroll down to the folder and hit right arrow
  7. Notice selection goes to the next menu (Bravery), not the submenu
• Screenshot if needed:
  
• Any related issues: Titlebar on Windows has a lot of wasted space #3036