1. MotionEvent.recycle() never set mRecycled to true so it couldn't actually
detect doubly-recycled events (unless the TRACK_RECYCLED_LOCATION debuging
flag was enabled).
2. MotionEvent.obtain() did not set mNext to null before returning the event
so it would unnecessarily retain a reference to other events in the
recycled event linked list until recycled again.
Change-Id: I93709c402d260691875f632dfc080a355f85fbb0
d28f4be870