Viewport doesn't regain focus after closing downloads-bar

[gulkily]

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

Describe the issue you encountered:
Clicking the Close/X button on the downloads bar doesn't return focus to the viewport.

Expected behavior:
Viewport should regain focus

• Platform (Win7, 8, 10? macOS? Linux distro?): macOS
• Brave Version: 0.11.5
• Steps to reproduce:
  1. Go to https://www.brave.com/
  2. Click "Get Brave"
  3. Save the file. Downloads-bar should appear at the bottom of the window
  4. Click the "X" (close) button on the downloads-bar
  5. Press the up/down keys on the keyboard

Expected: The browser viewport should have focus, and the page should scroll up and down when the up/down keys are pressed

Actual: Nothing happens when I press up/down keys, because the viewport doesn't have focus.

[cndouglas]

QA Steps (based on #3219 (comment) above):

1. Go to https://www.brave.com/
2. Click "Get Brave"
3. Save the file. Downloads-bar should appear at the bottom of the window
4. Click the "X" (close) button on the downloads-bar
5. Press the up/down keys on the keyboard
6. The content should scroll up and down