[ads] Ugly gradient on NTT video ad in Landscape mode

[btlechowski]

Follow up to #37653

Steps to Reproduce

1. Fresh install
2. Turn off WiFi and mobile network
3. Launch browser
4. Toggle Use Staging CRX components in Settings -> BraveCore Switches
5. Set rewards to staging
6. Close the browser
7. Turn on WiFi or mobile network
8. Launch Brave browser
9. Launch browser in Portrait orientation
10. Open New Tab Pages until a tab with New Tab Takeover video ad is opened
11. Wait till video stops playing
12. Rotate the phone to Landscape mode

Actual result:

Ugly gradient on NTT video ad in Landscape mode
Looks like we forgot to load a proper background image.

Expected result:

No ugly gradient on NTT video ad in Landscape mode

In landscape consider using the ad video keyframe and locking it to portrait (the keyframe image remains as in Portrait - it is not rotated)
So when user rotates the phone to portrait, the keyframe is already in portrait.

Reproduces how often: [Easily reproduced, Intermittent Issue]

Easily reproduced

Brave Version:

1.67.44 on iphone 13 pro max

cc @tmancey @aseren

[tmancey]

Closing as agreed we will not fix because if an RGB color is not specified in the filename the default is black #000000.