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Currently WebSocketChannel has methods subprotocol and extensions.
But they can be available only after the connection is established and
they don't change once set. Futhermore, there is didConnect notification
in WebSocketChannelClient.
This CL removes subprotocol and extensions from WebSocketChannel and
add them as WebSocketChannelClient::didConnect parameters.

BUG=384238
R=tyoshino

Review URL: https://codereview.chromium.org/334873002

git-svn-id: svn://svn.chromium.org/blink/trunk@176115 bbb929c8-8fbe-4397-9dbb-9b2b20218538