Downloads not being instantly displayed under "brave://downloads" until window resize

Test plan

See https://github.com/brave/brave-core/pull/3212

Description

Downloads are not being displayed under brave://downloads/ instantly at times. You’ll need to resize the current browser window for the entries to be displayed.

Couldn’t reproduce it with 76.0.3809.71 (Official Build) beta. Might be a regression with C76 as every channel but release is affected.

Steps to Reproduce

1. launch brave with a clean profile
2. visit https://www.thinkbroadband.com/download
3. download a few small file from the bottom of the page (I used Extra Small File (5MB) & Small File (10MB))
4. once the download has completed, click on Show All via the download bar

Actual result:

Expected result:

Downloads entries should be instantly displayed under brave://downloads/ without the need to resize the browser window.

Reproduces how often:

100% reproducible using the above STR.

Brave version (brave://version info)

Brave	0.69.77 Chromium: 76.0.3809.62 (Official Build) nightly (64-bit)
Revision	7b77856b3aa34d72f246d12340fc1ded8b2c0e83-refs/branch-heads/3809@{#798}
OS	Mac OS X

Version/Channel Information:

• Can you reproduce this issue with the current release? Not reproducible using 0.66.101 Chromium: 75.0.3770.142
• Can you reproduce this issue with the beta channel? Reproducible using 0.67.114 Chromium: 76.0.3809.62
• Can you reproduce this issue with the dev channel? Reproducible using 0.68.108 Chromium: 76.0.3809.62
• Can you reproduce this issue with the nightly channel? Reproducible using 0.69.77 Chromium: 76.0.3809.62

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? N/A
• Does the issue resolve itself when disabling Brave Rewards? N/A
• Is the issue reproducible on the latest version of Chrome? No, couldn’t reproduce using 76.0.3809.71 (Official Build) beta.

Miscellaneous Information:

CCing @brave/legacy_qa @rebron @bsclifton

[GeetaSarvadnya]

The issue is reproducible on Windows 10 x64

Brave	0.67.112 Chromium: 76.0.3809.62 (Official Build) beta (64-bit)
Revision	7b77856b3aa34d72f246d12340fc1ded8b2c0e83-refs/branch-heads/3809@{#798}
OS	Windows 10 OS Version 1803 (Build 17134.523)

[mhidro]

Happens every time I open the downloads tab. Just a blank screen until I hit F10 to open the inspect menu, which I guess resizes the window.

Version 0.67.125 Chromium: 76.0.3809.100 (Official Build) (64-bit) OS: Windows 7 SP2 and Windows 10.