We can't report negative values using histograms, so we split the data
up into two histograms

BUG=chromium:397026
LOG=n
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/572293002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23981 ce2b1a6d-e550-0410-aec6-3dcde31c8c00