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

chrome/browser/memory/tab_stats.h

Index: chrome/browser/memory/tab_stats.h
diff --git a/chrome/browser/memory/tab_stats.h b/chrome/browser/memory/tab_stats.h
index aa49e50e5b766531f778180a22de919b3fbea3d3..dcc979d7beeb88a46259c496894ec678f0ea58f9 100644
--- a/chrome/browser/memory/tab_stats.h
+++ b/chrome/browser/memory/tab_stats.h
@@ -22,6 +22,7 @@ struct TabStats {
   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;