unittests: fix main_test shutdown on macOS

The main_test hardening added a pre-Shutdown wait for
GetBrowserByIdentifier(MAIN_BROWSER_ID) to return None. All five macOS jobs
timed out there even though the JavaScript, popup, DevTools and handler
callbacks had completed.

CloseBrowser(True) starts an asynchronous native close and does not guarantee
that a synchronously created macOS browser reaches OnBeforeClose before
Shutdown. This matches upstream CEF issues chromiumembedded/cef#3469 and
chromiumembedded/cef#3810. cefpython removes the browser from its registry in
OnBeforeClose, so registry disappearance is not a portable pre-Shutdown
condition.

Remove only that close wait and restore the existing 25-iteration
MessageLoopWork grace period. Keep the condition-driven pre-close completion
gate that fixes the original Windows Python 3.14 timing failure, and let
cef.Shutdown() perform its existing final browser cleanup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: linesight

unittests/main_test.py

@@ -327,15 +327,10 @@ def shutdown_cef():
         del browser
         subtest_message("browser.CloseBrowser() ok")
 
-        # Browser destruction is asynchronous. Wait for the registry entry to
-        # disappear before checking callback assertions and shutting CEF down.
-        browser_closed = run_message_loop_until(
-            lambda: cef.GetBrowserByIdentifier(MAIN_BROWSER_ID) is None)
-        self.assertTrue(browser_closed,
-                        "Timed out waiting for the main browser to close")
-        # OnBeforeClose removes the Python registry entry before all native CEF
-        # teardown work has settled. Process a short grace period before
-        # Shutdown() to avoid racing those remaining tasks.
+        # CloseBrowser() is asynchronous. Process pending close work before
+        # checking callbacks and shutting CEF down. For synchronously created
+        # macOS browsers, OnBeforeClose may be deferred until Shutdown()
+        # (CEF issues #3469 and #3810).
         do_message_loop_work(25)
 
         # Asserts before shutdown