By Diane Bartz WASHINGTON (Reuters) – Any expansion by cable provider Comcast, including a deal with Charter Communications to split provider Time Warner Cable between them, would get a tough review from U.S. regulators, who might use the proposal to force Internet providers to treat all traffic equally, antitrust experts said. Charter Communications Inc reached out to Comcast Corp this week about teaming up to buy Time Warner Cable Inc, according to people familiar with the matter. Comcast is the top U.S. cable provider and video provider, Time Warner Cable is No. 2 and Charter is the fourth largest.