[WebSocket] Add a trivial optimization on permessage-deflate.

A very short message consits of one frame should not be compressed.
Fixed WebSocket Deflater unit tests.

BUG=163882
R=tyoshino

Review URL: https://codereview.chromium.org/28433002

git-svn-id: svn://svn.chromium.org/blink/trunk@159998 bbb929c8-8fbe-4397-9dbb-9b2b20218538