Add option to disallow the discarding of a tab that was previously discarded.

chrome/browser/memory/tab_stats.h

 // Copyright 2015 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_MEMORY_TAB_STATS_H_
 #define CHROME_BROWSER_MEMORY_TAB_STATS_H_
 
 #include <vector>
 
 #include "base/process/process.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 
 namespace memory {
 
 struct TabStats {
   TabStats();
   ~TabStats();
   bool is_app;            // Browser window is an app.
   bool is_internal_page;  // Internal page, such as NTP or Settings.
   bool is_playing_audio;
   bool is_pinned;
   bool is_selected;  // Selected in the currently active browser window.
   bool is_discarded;
+  int discard_count;
   base::TimeTicks last_active;
   base::ProcessHandle renderer_handle;
   int child_process_host_id;
   base::string16 title;
 #if defined(OS_CHROMEOS)
   int oom_score;
 #endif
   int64 tab_contents_id;  // Unique ID per WebContents.
 };
 
 typedef std::vector<TabStats> TabStatsList;
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_STATS_H_