Make memory pressure notifier configurable

base/memory/memory_pressure_monitor_chromeos.h

Index: base/memory/memory_pressure_monitor_chromeos.h
diff --git a/base/memory/memory_pressure_monitor_chromeos.h b/base/memory/memory_pressure_monitor_chromeos.h
index 5529c3b48a35857ddb1f923671a8850589354a5a..2df4edf95dc9b9ea0e40bac3e28c238705b567d2 100644
--- a/base/memory/memory_pressure_monitor_chromeos.h
+++ b/base/memory/memory_pressure_monitor_chromeos.h
@@ -65,7 +65,9 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // simple wrapper to base::MemoryPressureMonitor::Get.
   static MemoryPressureMonitor* Get();
 
- private:
+  void SetObserver(MemoryPressureMonitorObserver* observer) override;
+
+private:
   friend TestMemoryPressureMonitor;
   // Starts observing the memory fill level.
   // Calls to StartObserving should always be matched with calls to
@@ -88,6 +90,9 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // Get the memory pressure in percent (virtual for testing).
   virtual int GetUsedMemoryInPercent();
 
+  // Notify memory pressure level.
+  void Notify(MemoryPressureLevel level);
+
   // The current memory pressure.
   base::MemoryPressureListener::MemoryPressureLevel
       current_memory_pressure_level_;
@@ -107,6 +112,8 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // File descriptor used to detect low memory condition.
   ScopedFD low_mem_file_;
 
+  MemoryPressureMonitorObserver* observer_ = nullptr;
+
   base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);