Adding support for re-running of layout tests form the dashboard.

This allows the developer the ease of selecting specific layout tests which they want to re run from the convinience of a web page instead of terminal.

Review URL: https://codereview.chromium.org/502953003

git-svn-id: svn://svn.chromium.org/blink/trunk@182377 bbb929c8-8fbe-4397-9dbb-9b2b20218538