TimelinePanel: convert flame chart into icicle chart by fliping it bottom up.

BUG=316167
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/158883003

git-svn-id: svn://svn.chromium.org/blink/trunk@166826 bbb929c8-8fbe-4397-9dbb-9b2b20218538