Cancel URLRequest with an appropriate code when WebSocket handshake succeeds

To notify the NetworkDelegate of WebSocket handshake success explicitly, this
CL introduces a new net error and cancels the URLRequest with it.

BUG=663672

Review-Url: https://codereview.chromium.org/2628333003
Cr-Commit-Position: refs/heads/master@{#444523}
4 files changed