AndroidBaseWindow::GetZOrderLevel() to always return kNormal

This is the one-line fix that will make the test extension introduced
in http://crrev.com/c/6897417 work E2E.

Bug: 435478605
Change-Id: Ia58f4f9df3ca718fc0d971670e35cd730166f494
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6898172
Commit-Queue: Linyu He <linyuh@google.com>
Auto-Submit: Linyu He <linyuh@google.com>
Reviewed-by: Lijin Shen <lazzzis@google.com>
Commit-Queue: Lijin Shen <lazzzis@google.com>
Cr-Commit-Position: refs/heads/main@{#1508131}