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

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index 87ec5c0c462e513212928d1725d657302f2aab6f..37f2dcc02276d3f0cdeb5feeeac7456656a8f668 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -1162,13 +1162,15 @@ void ChromeBrowserMainParts::PreBrowserStart() {
   // On CrOS, it is always enabled. On other platforms, it's behind a flag for
   // now.
 #if defined(OS_CHROMEOS)
-  g_browser_process->GetOomPriorityManager()->Start();
+  g_browser_process->GetOomPriorityManager()->Start(false);
 #elif defined(OS_WIN) || defined(OS_MACOSX)
   const std::string group_name =
       base::FieldTrialList::FindFullName("AutomaticTabDiscarding");
   if (parsed_command_line().HasSwitch(switches::kEnableTabDiscarding) ||
       base::StartsWith(group_name, "Enabled", base::CompareCase::SENSITIVE)) {
-    g_browser_process->GetOomPriorityManager()->Start();
+    bool enabled_once = base::StartsWith(group_name, "Enabled_Once",
+                                         base::CompareCase::SENSITIVE);
+    g_browser_process->GetOomPriorityManager()->Start(enabled_once);
   }
 #endif
 }