Make memory pressure notifier configurable

base/memory/memory_pressure_monitor_win.h

Index: base/memory/memory_pressure_monitor_win.h
diff --git a/base/memory/memory_pressure_monitor_win.h b/base/memory/memory_pressure_monitor_win.h
index 5689ac6ac74a2befa9f2fac5d749948562953437..1fc4781a0b2f705a76e5bb804300da3dc7485caf 100644
--- a/base/memory/memory_pressure_monitor_win.h
+++ b/base/memory/memory_pressure_monitor_win.h
@@ -70,6 +70,8 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // Returns the critical pressure level free memory threshold, in MB.
   int critical_threshold_mb() const { return critical_threshold_mb_; }
 
+  void SetObserver(MemoryPressureMonitorObserver* observer) override;
+
  protected:
   // Internals are exposed for unittests.
 
@@ -112,6 +114,8 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   virtual bool GetSystemMemoryStatus(MEMORYSTATUSEX* mem_status);
 
  private:
+  void Notify(MemoryPressureLevel level);
+
   // Threshold amounts of available memory that trigger pressure levels. See
   // memory_pressure_monitor.cc for a discussion of reasonable values for these.
   int moderate_threshold_mb_;
@@ -132,6 +136,8 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // Ensures that this object is used from a single thread.
   base::ThreadChecker thread_checker_;
 
+  MemoryPressureMonitorObserver* observer_ = nullptr;
+
   // Weak pointer factory to ourself used for scheduling calls to
   // CheckMemoryPressure/CheckMemoryPressureAndRecordStatistics via |timer_|.
   base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;