Synthetic gestures today have a callback that completes when the gesture is finished dispatching. This leads to much flakiness since following events may start operating with the assumption all the effects of the gesture are completed. However, the gesture may not be fully propagated through the main and compositor threads, the pending and active trees. See the design doc for details: https://docs.google.com/document/d/18r8Ek8SCmJLdRf9WlvlOjonFRTTqWq2RomUhhXbkJZQ/edit#
Comment 1 by bokan@chromium.org
, Nov 6