Previously, the New WebSocket implementation in blink would treat an empty sub-protocol list as a vector containing a single empty string.

Empty WebSocket sub-protocols don't work, so send an empty vector instead.

BUG=312662

Review URL: https://codereview.chromium.org/50613002

git-svn-id: svn://svn.chromium.org/blink/trunk@160898 bbb929c8-8fbe-4397-9dbb-9b2b20218538