Fox Corp. has agreed to buy the streaming pioneer Roku in a cash-and-stock deal valued at approximately $22 billion, including debt. Roku will continue to be run as an open, partner-friendly platform, the companies said Monday, and there appears to be no immediate changes that customers will see. Fox and Roku said that the combined company will become the third-largest player in U. S. television by share of viewing. Media reports had surfaced on Friday that Roku was looking at its strategic a...