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..f1e6be5466ee52b3ae5f97c0984bd47cae03a5d2 100644
--- a/chrome/browser/memory/tab_manager.h
+++ b/chrome/browser/memory/tab_manager.h
@@ -178,6 +178,11 @@ 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 const int kDefaultTimeToFirstPurgeInSeconds = 1800;

[Wez, 2017/02/22 01:25:10]

nit: base::TimeDelta now has constexpr FromSeconds() helpers - could this be:

constexpr base::TimeDelta kDefaultTimeToFirstPurge =
base::TimeDelta::FromMinutes(30);

instead?

Otherwise, let's at least write it as 30 * 60 for clarity.

[tasak, 2017/02/22 04:18:46]

Done.

+
   // This is needed so WebContentsData can call OnDiscardedStateChange, and
   // can use PurgeAndSuspendState.
   friend class WebContentsData;