Since tooltips are always shown above a data point, it can extend above y=0 for some data points near the top of the first chart.
Created attachment 228155 [details] Fixes the bug
Created attachment 228157 [details] Rebased against ToT
Comment on attachment 228157 [details] Rebased against ToT Clearing flags on attachment: 228157 Committed r166701: <http://trac.webkit.org/changeset/166701>
All reviewed patches have been landed. Closing bug.