Add code to keep track of what fraction of pageviews are top sites.

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
===================================================================
--- chrome/browser/prerender/prerender_manager.h	(revision 98138)
+++ chrome/browser/prerender/prerender_manager.h	(working copy)
@@ -204,6 +204,8 @@
   // Adds a condition. This is owned by the PrerenderManager.
   void AddCondition(const PrerenderCondition* condition);
 
+  bool IsTopSite(const GURL& url) const;
+
  protected:
   // Test that needs needs access to internal functions.
   FRIEND_TEST_ALL_PREFIXES(PrerenderManagerTest, ExpireTest);
@@ -227,6 +229,8 @@
 
   class OnCloseTabContentsDeleter;
 
+  class MostVisitedSites;
+
   // Adds a prerender for |url| from referrer |referrer| initiated from the
   // RenderViewHost specified by |child_route_id_pair|. The |origin| specifies
   // how the prerender was added.
@@ -390,6 +394,8 @@
 
   scoped_ptr<PrerenderHistograms> histograms_;
 
+  scoped_ptr<MostVisitedSites> most_visited_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };