Schedule pings before frame loads in anchors.

If scheduled afterwards, a prerender navigation may kill the renderer
before the ping goes through.

BUG=302816

Review URL: https://codereview.chromium.org/26312002

git-svn-id: svn://svn.chromium.org/blink/trunk@159175 bbb929c8-8fbe-4397-9dbb-9b2b20218538