new tab background image and buttons are not spanned properly when browser window is minimized

[GeetaSarvadnya]

Description

new tab background image and buttons are not spanned properly when the browser window is minimized

Steps to Reproduce

1. Open brave 0.70.97
2. Open a few websites so that top tiles shown in NTP
3. Minimize the browser window
4. New tab background image and buttons are not spanned properly when the browser window is minimized

Actual result:

New tab background image and buttons are not spanned properly when the browser window is minimized

Expected result:

new tab background image and buttons are should be spanned properly when the browser window is minimized

Reproduces how often:

Always

Brave version (brave://version info)

Brave	0.70.97 Chromium: 77.0.3865.65 (Official Build) beta (64-bit)
Revision	87a331a3169cab563505fb44011058b904011ba1-refs/branch-heads/3865@{#726}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

Version/Channel Information:

• Can you reproduce this issue with the current release? No
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the dev channel? Yes
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? NA
• Does the issue resolve itself when disabling Brave Rewards? NA
• Is the issue reproducible on the latest version of Chrome? NA

Miscellaneous Information:

@brave/legacy_qa @karenkliu

[btlechowski]

Dupe of #5844