DaVita Buys U.S. Kidney Clinics for \$3 Bln  STOCKHOLM (Reuters) - DaVita Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=DVA.N target=/stocks/quickinfo/fullquote"&gt;DVA.N&lt;/A&gt; agreed to buy the  U.S. kidney-care clinics of Sweden's Gambro AB &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GAMBb.ST target=/stocks/quickinfo/fullquote"&gt;GAMBb.ST&lt;/A&gt; for  \$3.05 billion in a deal that would make it the top dialysis  services company in the United States.