[Desktop] JS errors in the console when opening a Private Window

[fmarier]

Description

There are unchecked runtime errors in the newtab page of private windows.

#1194 is similar but for Tor Windows.

Steps to Reproduce

1. Open a new Private Window
2. Open the devtools console

Actual result:

Expected result:

No errors.

Reproduces how often:

Always

Brave version (brave://version info)

Brave	1.11.69 Chromium: 83.0.4103.106 (Official Build) beta (64-bit)
Revision	ce7134bb3d95141cd18f1e65772a4247f282d950-refs/branch-heads/4103@{#694}
OS	Linux

[dentistformyeye]

When I turn off Rewards, only this shows up in the private newtab console.

Here's the result if I turn on rewards and open another private newtab (or return to an existing private newtab). I haven't been using Rewards; I don't know if that affects anything. The "Rewards service is not initialized" error repeats about once every 30 seconds. That "Unknown error" doesn't appear for me, so an update might have fixed it.

Brave	1.18.70 Chromium: 87.0.4280.101 (Official Build) (x86_64)
Revision	9407c80213cda69c2b7abcb4fa8e3f74488f4956-refs/branch-heads/4280@{#1807}
OS	macOS Version 10.15.7 (Build 19H2)