Comcast is expected to announce on Thursday an agreement to acquire Time Warner Cable for more than $45 billion in stock, a deal that would combine the biggest and second-biggest cable television operators in the country. For Comcast, which completed its acquisition of NBC Universal, the television and movie powerhouse, from General Electric less than a year ago, the latest deal would be its second big act to radically reshape the media landscape in the United States. And the merger is almost certain to bring to an end a protracted takeover battle that Charter Communications has been waging for Time Warner Cable. For Time Warner Cable, the deal provides a neat solution to its problems. It will receive just about the $160-a-share price it said was its true value, and possibly more. It will no longer have to slog ahead with a turnaround plan being run by a new chief executive, Rob Marcus. And it will allow it to become part of the company that is already the dominant force in cable television services. Despite combining the two largest cable operators in the country, a merger may have little impact on consumers.