It's not "The Zillow Center" yet, but listings portal and online real estate information marketplace Zillow Inc. has leased another floor in Seattle's fourth-largest high rise, a 42-story steel-and-glass tower originally built as the headquarters of Washington Mutual Inc., parent company of the failed savings and loan.All told, Zillow will occupy four floors 1301 Second Ave., the building formerly known as the WaMu Center -- just one less than the tenant the building is now named for, Russell Investments. Other tenants of the Russell Investments Center include Boeing, Nordstrom, Dendreon, and JP Morgan Chase, which picked up WaMu's assets from the FDIC in 2008.As designed for WaMu by architect NBBJ, the building was divided up into three-story "neighborhoods," each ...