Google Shares Slump on Revenue Outlook  SAN FRANCISCO (Reuters) - Shares of Google Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GOOG.O target=/stocks/quickinfo/fullquote"&gt;GOOG.O&lt;/A&gt;  fell almost 3 percent on Thursday, after the Web search leader  warned it could not sustain in revenue growth rate, a sign that  it could report disappointing fourth-quarter results.