Fix caption button alignment on Windows 7

[bsclifton]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Properly fixes #5069
(help needed manually testing- my VM is having issues)

Auditors: @bbondy, @jonathansampson

Test Plan:

1. Launch Brave on Windows 7
2. Look at the caption buttons; verify positioning looks OK (there may be rendering bugs, but those already exist)
3. Maximize window and ensure positioning is staying correct

[bsclifton]

Manually tested, worked great- will merge but would appreciate any feedback 😄