Fix WebSocketServer extension parser.

This CL makes the WebSocket server in net/server use the net/websockets
parser for parsing Sec-WebSocket-Extensions in the extension negotiation.

The new implementation validates the extension negotiation offer more
strictly than before. Specifically,

- Malformed Sec-WebSocket-Extensions header value causes connection failure.
 - Previously it was just ignored.
- Malformed permessage-deflate parameters are declined.
 - Previously part of such params were accepted partially.

BUG=523228

Review URL: https://codereview.chromium.org/1340523002

Cr-Commit-Position: refs/heads/master@{#351040}
12 files changed