Correct manual proxy selection for WebSockets.

When an HTTPS and/or HTTP proxy was manually configured, WebSocket
connections were mistakenly going direct to the origin server.

According to RFC6455, WebSocket connections should prefer SOCKS proxies,
then HTTPS, then HTTP proxies in that order. Fix the behaviour when
proxies are manually selected to match.

BUG=426736
TEST=net_unittests, manual
R=eroman@chromium.org

Review URL: https://codereview.chromium.org/710623002

Cr-Commit-Position: refs/branch-heads/2171@{#380}
Cr-Branched-From: 267aeeb8d85c8503a7fd12bd14654b8ea78d3974-refs/heads/master@{#297060}
3 files changed