Temporarily disable WebSocket over SPDY.

WebSocket over SPDY is not yet implemented in the new WebSocket
implementation. Temporarily disable attempts to re-use existing SPDY
connections for WebSocket connections or create new ones.

BUG=323846
TEST=net_unittests, wss://www.google.com/

Review URL: https://codereview.chromium.org/91263002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246597 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246597