Roll Flutter Engine from 505c720fd10f to 6cc678c528d1 (1 revision) (#136646)

https://github.com/flutter/engine/compare/505c720fd10f...6cc678c528d1

2023-10-16 jason-simmons@users.noreply.github.com Avoid a deadlock in the flutter_tester process when deleting the Impeller Vulkan context during shutdown (flutter/engine#46860)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC jsimmons@google.com,rmistry@google.com,zra@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter: https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

bin/internal/engine.version

-505c720fd10f7ee41f24a42fdf41c1c749058dad
+6cc678c528d14bc56685f3451ca64d1dfae8a1b0