TYPE_WINDOW_CONTENT_CHANGED should only be called for the root node of a subtree that has changed (NOT for every changed node in the subtree). Doing the latter causes a11y to become sluggish and unresponsive as Android processes the flood of events.

We are currently firing the event for every single changed node, which on big updates (e.g. scrolling through a list with lots of nodes) causes unresponsiveness.