Refactor ARC OOM handler code

chrome/browser/memory/tab_manager_delegate_chromeos.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_MEMORY_TAB_MANAGER_DELEGATE_CHROMEOS_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_DELEGATE_CHROMEOS_H_
 
 #include <memory>
 #include <string>
 #include <utility>
@@ skipping 23 matching lines @@
 // important.
 enum class ProcessType {
   // Conceptually, the system cannot have both FOCUSED_TAB and FOCUSED_APP at
   // the same time, but because Chrome cannot retrieve FOCUSED_APP status
   // synchronously, Chrome may still see both at the same time. When that
   // happens, treat FOCUSED_TAB as the most important since the (synchronously
   // retrieved) tab information is more reliable and up-to-date.
   FOCUSED_TAB = 1,
   FOCUSED_APP = 2,
 
-  VISIBLE_APP = 3,
+  // Important apps are protected in two ways: 1) Chrome never kills them, and
+  // 2) the kernel is still allowed to kill them, but their OOM adjustment
+  // scores are better than BACKGROUND_TABs and BACKGROUND_APPs.
+  IMPORTANT_APP = 3,
+
   BACKGROUND_TAB = 4,
   BACKGROUND_APP = 5,
   UNKNOWN_TYPE = 6,
 };
 
 // The Chrome OS TabManagerDelegate is responsible for keeping the
 // renderers' scores up to date in /proc/<pid>/oom_score_adj.
 class TabManagerDelegate : public aura::client::ActivationChangeObserver,
                            public content::NotificationObserver,
                            public chrome::BrowserListObserver {
@@ skipping 100 matching lines @@
   // Sets OOM score for processes in the range [|rbegin|, |rend|) to integers
   // distributed evenly in [|range_begin|, |range_end|).
   // The new score is set in |new_map|.
   void DistributeOomScoreInRange(
       std::vector<TabManagerDelegate::Candidate>::const_iterator begin,
       std::vector<TabManagerDelegate::Candidate>::const_iterator end,
       int range_begin,
       int range_end,
       ProcessScoreMap* new_map);
 
+  // Changes |candidates|' OOM scores to |score|. The new scores are set in
+  // |new_map|.
+  void SetOomScore(const std::vector<TabManagerDelegate::Candidate>& candidates,
+                   int score,
+                   ProcessScoreMap* new_map);
+
   // Initiates an oom priority adjustment.
   void ScheduleEarlyOomPrioritiesAdjustment();
 
   // Returns a TimeDelta object that represents a minimum delay for killing
   // the same ARC process again. ARC processes sometimes respawn right after
   // being killed. In that case, killing them every time is just a waste of
   // resources.
   static constexpr base::TimeDelta GetArcRespawnKillDelay() {
     return base::TimeDelta::FromSeconds(60);
   }
 
+  // The lowest OOM adjustment score that will make the process non-killable.
+  static const int kLowestOomScore;
+
   // Holds a reference to the owning TabManager.
   const base::WeakPtr<TabManager> tab_manager_;
 
   // Registrar to receive renderer notifications.
   content::NotificationRegistrar registrar_;
 
   // Timer to guarantee that the tab or app is focused for a certain amount of
   // time.
   base::OneShotTimer focus_process_score_adjust_timer_;
   // Holds the info of the newly focused tab or app. Its OOM score would be
@@ skipping 70 matching lines @@
   // reported if available memory is under the number.
   static int LowMemoryMarginKB();
 
   // Reads in an integer.
   static int ReadIntFromFile(const char* file_name, int default_val);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_DELEGATE_CHROMEOS_H_