[WebSocket] Run LayoutTests for the new implementation.

Turn on ExperimentalWebSocketEnabled runtime feature in LayoutTests.
Currently all failing tests are skipped, we should fix them later.
Tests for the old implementation run in virtual/stable/http/tests/websocket.

BUG=339373
R=ricea@chromium.org, tyoshino@chromium.org

Review URL: https://codereview.chromium.org/150133003

git-svn-id: svn://svn.chromium.org/blink/trunk@166281 bbb929c8-8fbe-4397-9dbb-9b2b20218538