Re-enable TopSites in PrerenderManager, this time duplicating the invariant

chrome/browser/prerender/prerender_tab_helper.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/prerender/prerender_tab_helper.h"
 
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/time.h"
 #include "chrome/browser/prerender/prerender_manager.h"
@@ skipping 292 matching lines @@
     UMA_HISTOGRAM_ENUMERATION("Prerender.HoverStats_TimeUntilClicked",
                               elapsed_ms, num_buckets);
   } else {
     UMA_HISTOGRAM_ENUMERATION("Prerender.HoverStats_TimeUntilDiscarded",
                               elapsed_ms, num_buckets);
   }
 
   current_hover_url_ = GURL();
 }
 
-bool PrerenderTabHelper::IsTopSite(const GURL& url) const {
+bool PrerenderTabHelper::IsTopSite(const GURL& url) {
   PrerenderManager* pm = MaybeGetPrerenderManager();
   return (pm && pm->IsTopSite(url));
 }
 
 }  // namespace prerender