Yes, he really said that. The Jerusalem Post reports:
Media bias is fueling Hillary Rodham Clinton’s presidential campaign and is burning Republicans, Donald Trump Jr. said on Wednesday, using a Holocaust reference to drive home his point. Speaking to Philadelphia Talk Radio 1210 WPHT, the Republican presidential nominee’s eldest son said that his father was held to a different standard from that of his rival.
“The media has been her number one surrogate in this,” Trump Jr. said. “Without the media, this wouldn’t even be a contest, but the media has built her up. They’ve let he slide on every indiscrepancy [sic], on every lie, on every DNC game trying to get Bernie Sanders out of this thing. If Republicans were doing that, they’d be warming up the gas chamber right now.”