Short browser freeze after joining rewards through Rewards Panel

[btlechowski]

It seems that after clicking Join Rewards from Rewards Panel, the browser freezes for few seconds.
This is a recent regression, introduced in 1.3.x.

Steps to Reproduce

1. Clean profile
2. Open Rewards Panel
3. Click JOIN REWARDS

Actual result:

Browser freezes for few seconds when wallet is created
The UI is not responsive, on hover effects aren't shown
The spinner next to CREATING WALLET is stuck

Expected result:

Browser does not freeze
The spinner next to CREATING WALLET is spinning

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Reproduced on

Brave	1.3.50 Chromium: 79.0.3945.56 (Official Build) nightly (64-bit)
Revision	73cc6bf591f792b99f8fc7cdfb8addedbd084bf8-refs/branch-heads/3945@{#788}
OS	Ubuntu 18.04 LTS

Not reproducible on

Brave	1.2.11 Chromium: 78.0.3904.108 (Official Build) dev (64-bit)
Revision	4b26898a39ee037623a72fcfb77279fce0e7d648-refs/branch-heads/3904@{#889}
OS	Ubuntu 18.04 LTS

Version/Channel Information:

• Can you reproduce this issue with the current release? no
• Can you reproduce this issue with the beta channel? no
• Can you reproduce this issue with the dev channel? no
• Can you reproduce this issue with the nightly channel? yes

cc @brave/legacy_qa @rebron @NejcZdovc @ryanml

[btlechowski]

No longer reproducible. I think it was fixed with Chromium 80.

Verification passed on

Brave	1.3.110 Chromium: 80.0.3987.78 (Official Build) (64-bit)
Revision	cb5aa81cb0a3a2c674b93bc7ffb34a86cd3b4802-refs/branch-heads/3987@{#752}
OS	Ubuntu 18.04 LTS