Add ServiceWorker timing information on the popup panel in DevTools's Network tab (1/2)

2nd patch: https://codereview.chromium.org/515753003/

BUG=401389
TEST=N/A

Review URL: https://codereview.chromium.org/515583005

git-svn-id: svn://svn.chromium.org/blink/trunk@182231 bbb929c8-8fbe-4397-9dbb-9b2b20218538