We still have some cases that low-level mouse events for a left-drag action is assumed to have button=Button::Left (similar to the UI MouseEvent spec). This is not true for mouse events from Android, which have button=Button::NoButton in such cases (similar to the PointerEvent spec).

We fix-up the JS-visible button value right before dispatching dom events so web is not affected. But internal event plumbing is still affected. E.g. we discovered one such case in MouseEventManager::handleMouseDraggedEvent() while working on  Issue 666060 .