Safety check Chrome cleaner child: fix test proxy type annotation

* Follow up to the last comment in crrev.com/c/2299742.

Bug: 1087263
Change-Id: I62e46bfc0fdc7053bd6acc3e43e599257a5834f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2328965Reviewed-by: Esmael Elmoslimany <aee@chromium.org>
Commit-Queue: Rainhard Findling <rainhard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794212}

chrome/test/data/webui/settings/safety_check_chrome_cleaner_test.js

@@ -65,7 +65,7 @@ function assertSafetyCheckChild({
 
 suite('SafetyCheckChromeCleanerUiTests', function() {
   /**
-   * @implements {BrowserProxy}
+   * @implements {ChromeCleanupProxy}
    * @extends {TestBrowserProxy}
    */
   let chromeCleanupBrowserProxy = null;