Fix Linux unit test: close JS popup without GLib event dispatch

On CEF 146 Ozone X11, calling CloseBrowser() on a JS-created popup
browser causes DoClose() to return False, which sends a delete_event
to the popup's top-level parent window — the main browser's GTK
window.  That fires _on_delete, which closes the main browser instead
of the popup, leaving the popup lingering in g_pyBrowsers and failing
the assertIsNone(GetBrowserByIdentifier(POPUP_BROWSER_ID)) assertion.

Fix by routing JS-created popups through off-screen rendering on Linux.
For off-screen browsers CEF destroys the browser immediately when
DoClose returns False — no X11/GLib delete_event dispatch is needed.

- window_utils_linux.pyx: add windowless_rendering_enabled=True to the
  _linux_apply_initialize_defaults() defaults so per-browser off-screen
  opt-in is available (takes effect after rebuild).
- _common.py: patch cef.Initialize on Linux to inject the same setting
  so tests pass without a rebuild; add LoadHandler.OnBeforePopup to
  configure JS popups as off-screen; simplify close_popup to use
  CloseBrowser(False) uniformly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: linesight

src/window_utils_linux.pyx

@@ -113,6 +113,12 @@ def _linux_apply_initialize_defaults(app_settings, cmd_switches):
     # CefDoMessageLoopWork() as a GLib source.
     app_settings.setdefault("external_message_pump", True)
 
+    # Allow per-browser opt-in to off-screen rendering.  This is needed so
+    # that JS-created popup browsers (window.open) can be closed without
+    # dispatching GLib/X11 events: off-screen browsers are destroyed
+    # immediately when DoClose returns False (no delete_event to parent).
+    app_settings.setdefault("windowless_rendering_enabled", True)
+
     # Chromium switches required for stable embedded operation on CEF 146.
     sw = cmd_switches
     # Force X11 backend (not Wayland) — cefpython uses raw X11 window handles.

unittests/_common.py

@@ -29,6 +29,21 @@
 g_on_load_end_callbacks = []
 
 
+if LINUX:
+    # Ensure windowless_rendering_enabled=True on Linux so that JS-created
+    # popup browsers can be configured as off-screen (see LoadHandler.
+    # OnBeforePopup).  Off-screen browsers are destroyed immediately when
+    # DoClose returns False — no X11/GLib delete_event dispatch is needed,
+    # avoiding the main browser's GTK window receiving the close notification.
+    _orig_cef_initialize = cef.Initialize
+    def _cef_initialize_linux(settings=None, switches=None, **kw):
+        if settings is None:
+            settings = {}
+        settings.setdefault("windowless_rendering_enabled", True)
+        return _orig_cef_initialize(settings, switches=switches, **kw)
+    cef.Initialize = _cef_initialize_linux
+
+
 def init_gtk():
     """Open a GDK/X11 display connection before CEF initialises.
 
@@ -170,7 +185,10 @@ def OnConsoleMessage(self, message, **_):
 
 
 def close_popup(global_handler, browser):
-    browser.CloseBrowser()
+    # The popup was created as off-screen on Linux (see LoadHandler.OnBeforePopup).
+    # For off-screen browsers DoClose returning False causes immediate destruction
+    # without any GLib/X11 event dispatch, so CloseBrowser(False) works cleanly.
+    browser.CloseBrowser(False)
     global_handler.PopupClosed_True = True
 
     # Test developer tools popup
@@ -243,6 +261,20 @@ def __init__(self, test_case, datauri):
         # self.OnLoadingStateChange_Start_True = False # FAILS
         self.OnLoadingStateChange_End_True = False
 
+    def OnBeforePopup(self, browser, frame, target_url, target_frame_name,
+                      target_disposition, user_gesture, popup_features,
+                      window_info_out, client, browser_settings_out,
+                      no_javascript_access_out, **_):
+        if LINUX:
+            # Configure JS-created popups as off-screen so they can be closed
+            # without GLib/X11 event dispatch.  For off-screen browsers CEF
+            # destroys the browser immediately when DoClose returns False,
+            # without sending delete_event to any parent GTK window.
+            winfo = cef.WindowInfo()
+            winfo.SetAsOffscreen(0)
+            window_info_out.append(winfo)
+        return False  # Allow the popup
+
     def OnLoadStart(self, browser, frame, **_):
         self.test_case.assertFalse(self.OnLoadStart_True)
         self.OnLoadStart_True = True