DevTools: instrument Ping request BEFORE it is sent.

Currently ping requests are instrumented after sending them.
As a result, response doesn't bring raw headers.

BUG=408363

Review URL: https://codereview.chromium.org/531733002

git-svn-id: svn://svn.chromium.org/blink/trunk@181285 bbb929c8-8fbe-4397-9dbb-9b2b20218538