Fix flaky OSR test: wait for OnAccessibilityLocationChange on slow CI

OnAccessibilityTreeChange and OnAccessibilityLocationChange are driven
by two separate renderer Mojo IPC messages.  The tree change fires when
the DOM is committed; the location change fires later, after layout
computes pixel positions.

On Linux CI (Xvfb + --in-process-gpu + software rendering), the
location-change IPC can arrive just past the standard 2-second message
loop window because each BeginFrame cycle requires a cross-thread
roundtrip between the in-process GPU/compositor thread and the UI
thread.  Windows CI is unaffected due to faster IPC dispatch margins.

Add a bounded 1-second extra pump that only activates when the flag is
not yet set, so passing runs pay nothing.

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

Author: linesight

unittests/osr_test.py

@@ -185,6 +185,12 @@ def test_osr(self):
         # Message loop
         run_message_loop()
 
+        # OnAccessibilityLocationChange arrives via a separate renderer IPC and
+        # can lag behind OnAccessibilityTreeChange on slow CI runners.  Give it
+        # up to 1 extra second before closing the browser.
+        if not accessibility_handler._OnAccessibilityLocationChange_True:
+            do_message_loop_work(100)
+
         # Close browser and clean reference
         browser.CloseBrowser(True)
         del browser