Identify methods that don't modify internal state and mark them const.

Change-Id: Ie63d93d51640bfb80dc02bb226d742c2f9be96d8
Remove unused member.

Change-Id: I8331251f77fb202375370a425e01862aa0f6310d
Create string from token array directly from ScTokenArray. Still WIP.

And make it re-entrant for thread safety. This method should not modify
the internal state of the token array object. The one with ScCompiler
is not re-entrant. Still some way to go.

Change-Id: I06de3637341727aef0963dddfb98527f415bf7fa