Integrate proptypes for our shared components.

- Fix unit tests.
- Fix linter errors.

src/components/PageHeaderToolbar.jsx

@@ -1,4 +1,5 @@
 import React, { Component } from 'react';
+import PropTypes from 'prop-types';
 import { Link } from 'react-router-dom';
 
 import { t } from '@lingui/macro';
@@ -126,4 +127,14 @@ class PageHeaderToolbar extends Component {
   }
 }
 
+PageHeaderToolbar.propTypes = {
+  isAboutDisabled: PropTypes.bool,
+  onAboutClick: PropTypes.func.isRequired,
+  onLogoutClick: PropTypes.func.isRequired,
+};
+
+PageHeaderToolbar.defaultProps = {
+  isAboutDisabled: false,
+};
+
 export default PageHeaderToolbar;