A written provision in any collective bargaining contract to settle by arbitration a controversy thereafter arising out of such contract or out of the refusal to perform the whole or any part thereof, or an agreement in writing to submit to arbitration an existing controversy arising out of such a contract, or such refusal, herein designated in this subchapter as “a written submission agreement,” shall be valid, irrevocable and enforceable, save upon such grounds, independent of the provisions for arbitration, as exist at law or in equity for the revocation of any contract.