[TabManager] Start function refactoring.

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 eef6d4d0351e243cab575989a2875caf4a4bf729..966c6163305129ee43e6b1c21f64e2e314eb79b2 100644
--- a/chrome/browser/memory/tab_manager.cc
+++ b/chrome/browser/memory/tab_manager.cc
@@ -165,15 +165,6 @@ void TabManager::Start() {
   if (!base::FeatureList::IsEnabled(features::kAutomaticTabDiscarding))
     return;
 
-  // Check the variation parameter to see if a tab be discarded more than once.
-  // Default is to only discard once per tab.
-  std::string allow_multiple_discards = variations::GetVariationParamValue(
-      features::kAutomaticTabDiscarding.name, "AllowMultipleDiscards");
-  if (allow_multiple_discards == "true")
-    discard_once_ = false;
-  else
-    discard_once_ = true;
-
   // Check the variation parameter to see if a tab is to be protected for an
   // amount of time after being backgrounded. The value is in seconds.
   std::string minimum_protection_time_string =
@@ -188,13 +179,11 @@ void TabManager::Start() {
             base::TimeDelta::FromSeconds(minimum_protection_time_seconds);
     }
   }
-
-#elif defined(OS_CHROMEOS)
-  // On Chrome OS, tab manager is always started and tabs can be discarded more
-  // than once.
-  discard_once_ = false;
 #endif
 
+  // Check if only one discard is allowed.
+  discard_once_ = ShouldOnlyDiscardOnce();
+
   if (!update_timer_.IsRunning()) {
     update_timer_.Start(FROM_HERE,
                         TimeDelta::FromSeconds(kAdjustmentIntervalSeconds),
@@ -561,8 +550,8 @@ void TabManager::PurgeAndSuspendBackgroundedTabs() {
   }
   if (purge_and_suspend_time <= 0)
     return;
-  auto purge_and_suspend_time_threshold = NowTicks() -
-      base::TimeDelta::FromSeconds(purge_and_suspend_time);
+  auto purge_and_suspend_time_threshold =
+      NowTicks() - base::TimeDelta::FromSeconds(purge_and_suspend_time);
   auto tab_stats = GetUnsortedTabStats();
   for (auto& tab : tab_stats) {
     if (!tab.render_process_host->IsProcessBackgrounded())
@@ -858,6 +847,21 @@ bool TabManager::DiscardTabImpl() {
   return false;
 }
 
+// Check the variation parameter to see if a tab can be discarded only once or
+// multiple times.
+// Default is to only discard once per tab.
+bool TabManager::ShouldOnlyDiscardOnce() {
+#if defined(OS_CHROMEOS)
+  // On Chrome OS, tab manager is always started and tabs can be discarded more

[Georges Khalil, 2016/05/17 15:18:01]

nit: change this comment to 
On Chrome OS, tabs can always be discarded more than once.

[Anderson Silva, 2016/05/17 15:34:06]

Acknowledged.

+  // than once.
+  return false;
+#endif

[Georges Khalil, 2016/05/17 15:18:01]

You need an #elif otherwise you'll get a warning on Chrome OS (unreachable
code).

[Anderson Silva, 2016/05/17 15:34:06]

Acknowledged.

+
+  std::string allow_multiple_discards = variations::GetVariationParamValue(
+      features::kAutomaticTabDiscarding.name, "AllowMultipleDiscards");
+  return (allow_multiple_discards == "false");

[Georges Khalil, 2016/05/17 15:18:01]

This should be:
return (allow_multiple_discards != "true");

That's because the default behavior is to discard only once so if the variation
doesn't exist, we return true. Add a comment to that effect:
On all other platforms, default to discarding only once unless otherwise
specified by the variation parameter.

[Anderson Silva, 2016/05/17 15:34:07]

Acknowledged.

+}
+
 // Things to collect on the browser thread (because TabStripModel isn't thread
 // safe):
 // 1) whether or not a tab is pinned