The delta value in the chart pane sometimes doens't show '+' for a positive delta

The delta value in the chart pane sometimes doens't show '+' for a positive delta
https://bugs.webkit.org/show_bug.cgi?id=141340

Reviewed by Andreas Kling.

The bug was caused by computeStatus prefixing the value delta with '+' if it's greater than 0 after
it had already been formatted. Fixed the bug by using a formatter that always emits a sign symbol.

* public/v2/app.js:
(App.Pane.computeStatus):
(App.createChartData):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179766 268f45cc-cd09-0410-ab3c-d52691b4dbfc