Make time_to_first_suspension's default 1800sec

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 0e2d48a8b0bd40bec5a18596dd952e9e51bb1bbe..c384b7e054b07fa3eb20ad6b794bd748fcaf5665 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -178,6 +178,12 @@ class TabManager : public TabStripModelObserver {
   FRIEND_TEST_ALL_PREFIXES(TabManagerTest, TabManagerBasics);
   FRIEND_TEST_ALL_PREFIXES(TabManagerWebContentsDataTest, PurgeAndSuspendState);
 
+  // The time of the first purging after a renderer is backgrounded.
+  // The initial value was chosen because most of users activate backgrounded
+  // tabs within 30 minutes. (c.f. Tabs.StateTransfer.Time_Inactive_Active)
+  static constexpr base::TimeDelta kDefaultTimeToFirstPurge =
+      base::TimeDelta::FromMinutes(30);
+
   // This is needed so WebContentsData can call OnDiscardedStateChange, and
   // can use PurgeAndSuspendState.
   friend class WebContentsData;