Cope with missing hover-in event in stats tables row highlighting

We reliably miss a hover-in event if the pointer is over a row when
we attach the highlighting code to hover events. The simple fix is
to just ignore hover-out events before we have received the hover-in
event first.

Bug: 36692
Change-Id: I15e323a588a9098969d094095bd9f85cfcd9f91b
Merge "Cope with missing hover-in event in stats tables row highlighting"