Make time_to_first_suspension's default 1800sec

chrome/browser/memory/tab_manager.cc

Index: chrome/browser/memory/tab_manager.cc
diff --git a/chrome/browser/memory/tab_manager.cc b/chrome/browser/memory/tab_manager.cc
index 56aae1cde41797cce72fee5f6f612945155a9911..78f6d2d5d2a28f2b6f56488d00aa7d005fee50c0 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -230,7 +230,7 @@ void TabManager::Start() {
   if (purge_and_suspend_time.empty() ||
       !base::StringToUint(purge_and_suspend_time,
                           &time_to_first_suspension_sec))
-    time_to_first_suspension_sec = 108000;
+    time_to_first_suspension_sec = 1800;

[Wez, 2017/02/17 07:39:17]

Please define this as a constant e.g. kDefaultTimeToFirstSuspendSeconds and
define it with a comment explaining why we have chosen this value.

[tasak, 2017/02/17 12:36:06]

Changed to use kDefaultTimeToFirstSuspensionSeconds, and add a comment.
However, I think, there is no strong reason why the default value is 30
minutes...

[Wez, 2017/02/17 19:03:14]

There doesn't need to be a _string_ reason, just some rationale at all - e.g.
did we choose the value to purge "soon" after a tab becomes idle, but not so
soon that simply switching tabs will cause jank?

[Wez, 2017/02/17 19:26:32]

s/string/strong ;)

   time_to_first_suspension_ =
       base::TimeDelta::FromSeconds(time_to_first_suspension_sec);
 }