Prerender: Remove deprecated prerender experiment histograms.

chrome/browser/prerender/prerender_manager.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_MANAGER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 183 matching lines @@
   // outside that range indicating that it doesn't apply.
   void RecordPerceivedPageLoadTime(
       Origin origin,
       NavigationType navigation_type,
       base::TimeDelta perceived_page_load_time,
       double fraction_plt_elapsed_at_swap_in,
       const GURL& url);
 
   static PrerenderManagerMode GetMode();
   static void SetMode(PrerenderManagerMode mode);
-  static const char* GetModeString();
   static bool IsPrerenderingPossible();
   static bool ActuallyPrerendering();
   static bool IsControlGroup();
   static bool IsNoUseGroup();
   static bool IsNoStatePrefetch();
 
   // Query the list of current prerender pages to see if the given web contents
   // is prerendering a page. The optional parameter |origin| is an output
   // parameter which, if a prerender is found, is set to the Origin of the
   // prerender |web_contents|.
@@ skipping 348 matching lines @@
   // Set of process hosts being prerendered.
   using PrerenderProcessSet = std::set<content::RenderProcessHost*>;
   PrerenderProcessSet prerender_process_hosts_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_