Make three simultanious prerenders the default maximum in Canary and Dev only.

chrome/browser/prerender/prerender_histograms.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_
 
 #include <string>
 
 #include "base/time.h"
@@ skipping 61 matching lines @@
                          uint8 experiment_id,
                          PrerenderContents::MatchCompleteStatus mc_status,
                          FinalStatus final_status) const;
 
   // To be called when a new prerender is added.
   void RecordPrerender(Origin origin, const GURL& url);
 
   // To be called when a new prerender is started.
   void RecordPrerenderStarted(Origin origin) const;
 
+  // To be called when we know how many prerenders are running after starting
+  // a prerender.
+  void RecordConcurrency(size_t prerender_count) const;
+
   // Called when we swap in a prerender.
   void RecordUsedPrerender(Origin origin) const;
 
   // Record the time since a page was recently visited.
   void RecordTimeSinceLastRecentVisit(base::TimeDelta time) const;
 
   // Record a percentage of pixels of the final page already in place at
   // swap-in.
   void RecordFractionPixelsFinalAtSwapin(double fraction) const;
 
@@ skipping 46 matching lines @@
   // start recording events before the first prerender occurs.
   bool seen_any_pageload_;
   bool seen_pageload_started_after_prerender_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderHistograms);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_