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/threading/non_thread_safe.h"
 #include "base/time.h"
 #include "googleurl/src/gurl.h"
 
 class PrerenderContents;
 class Profile;
 class TabContents;
 
 // PrerenderManager is responsible for initiating and keeping prerendered
 // views of webpages.
 class PrerenderManager : public base::RefCounted<PrerenderManager>,
                          private base::NonThreadSafe {
  public:
+  // SessionType is used in a UMA_HISTOGRAM, so please do not add in the
+  // middle.
+  enum SessionType {
+    PRERENDERING_OFF,
+    PRERENDERING_ON,
+    PRERENDERING_SESSION_TYPE_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,
   // determines whether a preloaded version of the URL can be used,
   // and substitutes the prerendered RVH into the TabContents.  Returns
   // whether or not a prerendered RVH could be used or not.
   bool MaybeUsePreloadedPage(TabContents* tc, const GURL& url);
 
   // Allows PrerenderContents to remove itself when prerendering should
   // be cancelled.  Also deletes the entry.
   void RemoveEntry(PrerenderContents* entry);
 
   // Retrieves the PrerenderContents object for the specified URL, if it
   // has been prerendered.  The caller will then have ownership of the
   // PrerenderContents object and is responsible for freeing it.
   // Returns NULL if the specified URL has not been prerendered.
   PrerenderContents* GetEntry(const GURL& url);
 
   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 SessionType GetSessionType();
+
  protected:
   virtual ~PrerenderManager();
 
  private:
   friend class base::RefCounted<PrerenderManager>;
   struct PrerenderContentsData;
 
   bool IsPrerenderElementFresh(const base::Time start) const;
   void DeleteOldEntries();
   virtual base::Time GetCurrentTime() const;
@@ skipping 12 matching lines @@
   // 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;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_MANAGER_H_