The right hand side of main chart appears to be cut off as you zoom out on v3 UI

The right hand side of main chart appears to be cut off as you zoom out on v3 UI
https://bugs.webkit.org/show_bug.cgi?id=152778

Reviewed by Antti Koivisto.

Add a padding on x-axis after the end time to make the main chart more easily interactive.

* public/v3/components/time-series-chart.js:
(TimeSeriesChart.prototype._computeHorizontalRenderingMetrics):

* public/v3/pages/page-with-charts.js:
(PageWithCharts.mainChartOptions): Add a padding of 5px at the end of x-axis.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@194653 268f45cc-cd09-0410-ab3c-d52691b4dbfc