Add histogram to track prerender sessions

chrome/browser/prerender/prerender_manager.h

 // 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.
 
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_
 #pragma once
 
 #include <list>
 #include <vector>
 
 #include "base/ref_counted.h"
 #include "base/scoped_ptr.h"
 #include "base/time.h"
 #include "chrome/browser/prerender/prerender_contents.h"
 #include "googleurl/src/gurl.h"
 
 class Profile;
 class TabContents;
 
 // PrerenderManager is responsible for initiating and keeping prerendered
 // views of webpages.
 class PrerenderManager : public base::RefCounted<PrerenderManager> {
  public:
+  // PrerenderManagerMode is used in a UMA_HISTOGRAM, so please do not
+  // add in the middle.
   enum PrerenderManagerMode {
     PRERENDER_MODE_DISABLED,
     PRERENDER_MODE_ENABLED,
     PRERENDER_MODE_EXPERIMENT_CONTROL_GROUP,
-    PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP
+    PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP,
+    PRERENDER_MODE_MAX
   };
 
   // Owned by a Profile object for the lifetime of the profile.
   explicit PrerenderManager(Profile* profile);
 
   // Preloads the URL supplied.  alias_urls indicates URLs that redirect
   // to the same URL to be preloaded.
   void AddPreload(const GURL& url, const std::vector<GURL>& alias_urls);
 
   // For a given TabContents that wants to navigate to the URL supplied,
@@ skipping 12 matching lines @@
   // Returns NULL if the specified URL has not been prerendered.
   PrerenderContents* GetEntry(const GURL& url);
 
   void RecordPerceivedPageLoadTime(base::TimeDelta pplt);
 
   base::TimeDelta max_prerender_age() const { return max_prerender_age_; }
   void set_max_prerender_age(base::TimeDelta td) { max_prerender_age_ = td; }
   unsigned int max_elements() const { return max_elements_; }
   void set_max_elements(unsigned int num) { max_elements_ = num; }
 
+  static PrerenderManagerMode GetMode();
+  static void SetMode(PrerenderManagerMode mode);
+
  protected:
   virtual ~PrerenderManager();
 
   void SetPrerenderContentsFactory(
       PrerenderContents::Factory* prerender_contents_factory);
 
  private:
   // Test that needs needs access to internal functions.
   friend class PrerenderBrowserTest;
 
@@ skipping 21 matching lines @@
   std::list<PrerenderContentsData> prerender_list_;
 
   // Default maximum permitted elements to prerender.
   static const unsigned int kDefaultMaxPrerenderElements = 1;
 
   // Default maximum age a prerendered element may have, in seconds.
   static const int kDefaultMaxPrerenderAgeSeconds = 20;
 
   scoped_ptr<PrerenderContents::Factory> prerender_contents_factory_;
 
-  PrerenderManagerMode mode_;
+  static PrerenderManagerMode mode_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_