Make purge-and-suspend-time finch experiment parameter

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 207ae5d7bfd86e6a6951965eb4f1f980d4014ff3..b6062ab348a7fc4de577743cd6eddddf47e7aff5 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -221,6 +221,18 @@ void TabManager::Start() {
     }
   }
 #endif
+  // purge-and-suspend param is used for Purge+Suspend finch experiment
+  // in the following way:
+  // https://docs.google.com/document/d/1hPHkKtXXBTlsZx9s-9U17XC-ofEIzPo9FYbBEc7PPbk/edit?usp=sharing
+  std::string purge_and_suspend_time = variations::GetVariationParamValue(
+      "PurgeAndSuspend", "purge-and-suspend-time");
+  unsigned time_to_first_suspension_sec;
+  if (purge_and_suspend_time.empty() ||
+      !base::StringToUint(purge_and_suspend_time,
+                          &time_to_first_suspension_sec))
+    time_to_first_suspension_sec = 108000;

[Wez, 2017/02/15 22:22:52]

There doesn't seem to be any explanation here, or in the linked document, of why
30 hours is a good time-to-first-suspension?

+  time_to_first_suspension_ =
+      base::TimeDelta::FromSeconds(time_to_first_suspension_sec);
 }
 
 void TabManager::Stop() {
@@ -731,21 +743,7 @@ TabManager::PurgeAndSuspendState TabManager::GetNextPurgeAndSuspendState(
 }
 
 void TabManager::PurgeAndSuspendBackgroundedTabs() {
-  const base::CommandLine& command_line =
-      *base::CommandLine::ForCurrentProcess();
-  if (!command_line.HasSwitch(switches::kPurgeAndSuspendTime))
-    return;
-  int purge_and_suspend_time = 0;
-  if (!base::StringToInt(
-          command_line.GetSwitchValueASCII(switches::kPurgeAndSuspendTime),
-          &purge_and_suspend_time)) {
-    return;
-  }
-  if (purge_and_suspend_time <= 0)
-    return;
   base::TimeTicks current_time = NowTicks();
-  base::TimeDelta time_to_first_suspension =
-      base::TimeDelta::FromSeconds(purge_and_suspend_time);
   auto tab_stats = GetUnsortedTabStats();
   for (auto& tab : tab_stats) {
     if (!tab.render_process_host->IsProcessBackgrounded())
@@ -766,7 +764,7 @@ void TabManager::PurgeAndSuspendBackgroundedTabs() {
            tab.last_hidden <
                GetWebContentsData(content)->LastPurgeAndSuspendModifiedTime());
     PurgeAndSuspendState next_state = GetNextPurgeAndSuspendState(
-        content, current_time, time_to_first_suspension);
+        content, current_time, time_to_first_suspension_);
     if (current_state == next_state)
       continue;