Measure subresource requests for "legacy" protocols and credentialed URLs.

This patch treats adds a UseCounter for subresource requests for protocols like
FTP and Gopher from "webby" security origins. It also adds a counter for URLs
with embedded credentials. Depending on the numbers, we may be able to take more
drastic action than measurement in the future.

BUG=413586

Review URL: https://codereview.chromium.org/568743002

git-svn-id: svn://svn.chromium.org/blink/trunk@182068 bbb929c8-8fbe-4397-9dbb-9b2b20218538