gui_toolkit 0.57.1

Fixed

• The screencast could miss its last frame: input sent while a capture was coming back, or the last step of an animation, counted as nothing changed. Tests: the end-to-end run waits for the frames to stop instead of fixed delays, and what still depends on a machine's timing (a first frame, the last one) is said as FLAKY without failing it; frames that never stop still fail it.
• Closing Chrome's DevTools could leave a window on freed memory: the connection was freed while the DOM side still held it, so the edits could stay and the program could hang. They now go with the client, every time.