WebSocketChannelClient methods should be callable even when suspended.

WebSocketChannelClient methods in WebSocket should be callable even when it is
suspended or stopped.
We introduce WebSocket::EventQueue to queue events during the WebSocket is
suspended.

BUG=302898

Review URL: https://codereview.chromium.org/36553003

git-svn-id: svn://svn.chromium.org/blink/trunk@160424 bbb929c8-8fbe-4397-9dbb-9b2b20218538