Fix the details of InvalidStateError thrown when send() is called in CONNECTING state.

CONNECTING is initial state. So, "already" in the detail string is
inapproprite. Use "still" and factor out the common code as bonus.

Also fix incorrect detail string in closeInternal().

BUG=none

Review URL: https://codereview.chromium.org/79143004

git-svn-id: svn://svn.chromium.org/blink/trunk@162519 bbb929c8-8fbe-4397-9dbb-9b2b20218538