Make purge-and-suspend-time finch experiment parameter

chrome/browser/memory/tab_manager.h

Index: chrome/browser/memory/tab_manager.h
diff --git a/chrome/browser/memory/tab_manager.h b/chrome/browser/memory/tab_manager.h
index e4d7fee434a3d3333cecdd2cf5172aea2bcec0b0..55b6d1d98314f0adcdd087b0c64379b453df24e5 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -366,6 +366,9 @@ class TabManager : public TabStripModelObserver {
   // backgrounded.
   base::TimeDelta minimum_protection_time_;
 
+  // A backgrounded renderer will be suspended when this time passes.
+  base::TimeDelta time_to_first_suspension_;
+
 #if defined(OS_CHROMEOS)
   std::unique_ptr<TabManagerDelegate> delegate_;
 #endif