Adding flag to specify the used memory pressure strategy

base/chromeos/memory_pressure_observer_chromeos.h

 // Copyright 2014 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 BASE_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_
 #define BASE_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_
 
 #include "base/base_export.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/memory/weak_ptr.h"
 #include "base/timer/timer.h"
 
 namespace base {
 
 class TestMemoryPressureObserver;
 
 ////////////////////////////////////////////////////////////////////////////////
 // MemoryPressureObserverChromeOS
 //
 // A class to handle the observation of our free memory. It notifies the
 // MemoryPressureListener of memory fill level changes, so that it can take
 // action to reduce memory resources accordingly.
 //
 class BASE_EXPORT MemoryPressureObserverChromeOS {
  public:
   using GetUsedMemoryInPercentCallback = int (*)();
 
-  MemoryPressureObserverChromeOS();
+  enum MemoryPressureThresholds {
+    DEFAULT_THRESHOLDS = 0,             // Use the default.

[Charlie Reis, 2015/01/21 17:42:05]

These names and comments are confusing to me.  Normal, aggressive, moderate, and
critical could all be names on the same scale, so please add a comment
explaining how they relate.

Also, I'm not sure about the conventions in this code, but the content module
tends to name enums differently:
http://www.chromium.org/developers/content-module/content-api
"enum values should start with the name of the type, i.e. PAGE_TRANSITION_LINK
in the content::PageTransition enum"

[Mr4D (OOO till 08-26), 2015/01/21 18:52:14]

Done.

+    NORMAL_THRESHOLDS = 1,              // Use both thresholds as normal.
+    AGGRESSIVE_MODERATE_THRESHOLD = 2,  // Use an aggressive moderate threshold.
+    AGGRESSIVE_CRITICAL_THRESHOLD = 3,  // Use an aggressive critical threshold.
+    AGGRESSIVE_THRESHOLDS = 4           // Both thresholds are aggressive.
+  };
+
+  explicit MemoryPressureObserverChromeOS(MemoryPressureThresholds thresholds);
   virtual ~MemoryPressureObserverChromeOS();
 
   // Redo the memory pressure calculation soon and call again if a critical
   // memory pressure prevails. Note that this call will trigger an asynchronous
   // action which gives the system time to release memory back into the pool.
   void ScheduleEarlyCheck();
 
   // Get the current memory pressure level.
   base::MemoryPressureListener::MemoryPressureLevel GetCurrentPressureLevel() {
     return current_memory_pressure_level_;
@@ skipping 23 matching lines @@
       current_memory_pressure_level_;
 
   // A periodic timer to check for resource pressure changes. This will get
   // replaced by a kernel triggered event system (see crbug.com/381196).
   base::RepeatingTimer<MemoryPressureObserverChromeOS> timer_;
 
   // To slow down the amount of moderate pressure event calls, this counter
   // gets used to count the number of events since the last event occured.
   int moderate_pressure_repeat_count_;
 
+  // The thresholds for moderate and critical pressure.
+  const int moderate_pressure_threshold_;
+  const int critical_pressure_threshold_;
+
   base::WeakPtrFactory<MemoryPressureObserverChromeOS> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureObserverChromeOS);
 };
 
 }  // namespace base
 
 #endif  // BASE_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_