Disallow connecting an insecure WebSocket from a secure page.

This is revised version of yhirano@'s patch:
https://src.chromium.org/viewvc/blink?revision=165922&view=revision

The check is done inside
MainThreadWebSocketChannel/NewWebSocketChannelImpl since it's easy to
access the LocalFrame instance.

A worker test is added to ensure it works even in a worker.

BUG=85271

Review URL: https://codereview.chromium.org/222153002

git-svn-id: svn://svn.chromium.org/blink/trunk@172727 bbb929c8-8fbe-4397-9dbb-9b2b20218538