Oilpan: Move WebSocket and WebSocket::EventQueue to oilpan's heap

This is one of incremental steps to move modules/websockets to oilpan's heap.

BUG=340522

Review URL: https://codereview.chromium.org/259193003

git-svn-id: svn://svn.chromium.org/blink/trunk@172956 bbb929c8-8fbe-4397-9dbb-9b2b20218538