Fixed window border on Windows: focused blue / unfocused gray (broke ~0.15.0)

[bsclifton]

Test plan

1. Launch Brave on Windows and ensure the window has a blue-ish border
2. Make the window small enough that you focus on another item (like empty doc in notepad) and still see Brave
3. When Brave loses focus, it should get a gray border
4. When Brave gets focus again, it should get back the blue-ish border

Original issue description

Windows will usually have the blue border when a window is focused which turns into a gray border when the window loses focus. This functionality was broken with 901d5db and was never restored. The single window action onFocusChanged was split out into onFocus and onBlur, but nothing calls them

[srirambv]

Still right bluish border is missing on 0.15.301. @bsclifton is this still expected behavior on Windows?

[bsclifton]

@srirambv yes- this is captured with #6698