brave-browser: Crash when clicking on the Brave or Brave Rewards icons with `extensions-toolbar-menu` enabled

Test plan

See https://github.com/brave/brave-core/pull/4065

Description

Brave crashes whenever I click on the Brave or Brave Rewards icons on the address bar. brave://crashes is empty.

Steps to Reproduce

1. Open Brave
2. Click on the Brave or Brave Rewards icon

Actual result:

Brave crashes

Expected result:

Brave should not crash. The proper dialog (either the Shields dialog or the Brave Rewards dialog, depending on which icon was clicked) should show up.

Reproduces how often:

Happens every time

Brave version (brave://version info)

Brave: 0.67.124 Chromium: 76.0.3809.100 (Official Build) (64-bit) Revision: ed9d447d30203dc5069e540f05079e493fc1c132-refs/branch-heads/3809@{#990} OS: Linux Window manager: KDE Plasma 5.16.4-0ubuntu1

$ lsb_release -a
LSB Version:    core-10.2019031300ubuntu1-noarch:printing-10.2019031300ubuntu1-noarch:security-10.2019031300ubuntu1-noarch
Distributor ID: Ubuntu
Description:    Ubuntu 19.04
Release:        19.04
Codename:       disco
You                                                                                                                                                            

$ uname -a
Linux tumbolia 5.0.0-23-generic #24-Ubuntu SMP Mon Jul 29 15:36:44 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

Version/Channel Information:

I have not tried it on any other channels. However, it happened on the previous version I got from the https://brave-browser-apt-release.s3.brave.com PPA, possibly on even earlier versions, but I haven’t been keeping track of how often it is updated. It has been happening for a few weeks now.

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?

I cannot disable Brave Shields due to this issue

• Does the issue resolve itself when disabling Brave Rewards?

I cannot disable Brave Rewards due to this issue

• Is the issue reproducible on the latest version of Chrome?

Does not apply to Chrome, this is Brave-specific functionality

Miscellaneous Information: